Sans is a MONSTER and not a HUMAN, so he doesn't follow HUMAN biology like a HUMAN skeleton. Same with Gaster and Papyrus.  

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Of course the moment the twins were all wrapped up and warm, it was inevitable they were going to want to go bursting out of the door, into the freezing cold snow, with the two parents closely following behind, after barely being given the chance to put their own shoes on. Sans didn't really have to wrap up that much, being a skeleton and all, but Frisk made the effort to wrap herself and her two children up in a warm hat, with scarves and gloves. "don't run off too far ahead!" Sans was already yelling to Leo and Luna, who were still staying fairly close to their mom and dad, but they were also running around in the snow throwing snowballs at each other. Preferably, Sans - being as overprotective as he was - would have wanted to hold their hands, so they stayed very close. But of course, it would be hard to fight against two kids who just wanted to have fun in the snow. At least Leo seemed like he was enjoying himself.

"It makes me glad, they seem so happy..." Frisk murmured to the skeleton, as she held his hand while they walked down the path together, feeling the blanket of snow beneath their feet crunching with each step. It made such a satisfying noise, each and every time their shoes compressed against the ground. "They hadn't smiled that much, in the time we had been apart." Frisk went on, still watching the two closely who were still ahead of them, running and playing. Sans was quiet, but he knew what she was talking about. Whenever he did go to see the kids in the weeks that him and Frisk weren't a couple, they definitely had been more glum than normal. It was one of those extra things that had made him feel so damn guilty about his decision; even if Leo and Luna hadn't completely understood what was going on, it had been very obvious that it had been affecting them negatively. 

The last thing Sans ever wanted was to make a negative impact on his children's lives.

"yeah... i see what ya mean." Sans agreed with a nod, gently squeezing Frisk's hand once he said that. He had no plans to go anywhere, after the hell they went through, by just being apart from one another. Being apart from one another, was like someone stopping a human from doing one of the necessities they needed - like breathing. If you starved a person of the ability to breathe, it would be inevitable they'd die out without it - because it was needed. Sans didn't like to think he would have done anything drastic, if he continued to allow himself to feel so damn loopy without Frisk at his side, but he just knew that... Things would have been hard. Even with two kids in the picture. If they weren't happy, and Sans couldn't make them happy, then... It would have all just gone downhill from there.

It took a lot of starting and stopping for the mother and father, as every now and then they did end up catching up to their two children, who would either stop to make snow angels, or just to have more snowball fights. Because of this, it took a little longer to make it to the mall nearby, but neither Sans nor Frisk minded, because their kids were having a lot of fun, and that's truly what made the skeleton and human smile. Once they were in the mall though, that's when Sans held Leo's and Luna's hands, considering the place was rather busy, and the last thing they wanted was to lose their children in the sea of people. 

"Hey! Look, there's Santwa!" Luna was already pointing to an area in the mall, where it looked like there was a long line of people, and at the front of that long line, was a big man, dressed in red and white, (of course), with a white fluffy beard. A small child was already sitting on Santa's lap, seeming to say what they wanted for Christmas. "Can we go see him, please, please!" Luna pleaded. Leo on the other hand was quiet, but it was clear by the glint in his eyes that even he was excited to see the plump man dressed in red.

"I'm sure daddy wouldn't mind taking you to see Santa. Mommy has got to run a couple of errands." Frisk said, smiling towards her fiance who had already agreed to taking his two kids to see Santa - even if the line was pretty long. Frisk needed enough time to get presents anyway, so this would likely be enough to keep Leo and Luna distracted for awhile. Maybe for an hour or two judging by how long the line was. "Have fun, okay? Make sure you be good for Santa." Frisk said, kneeling down to kiss each of her children on the head, before she also kissed Sans on the cheekbone.

"see ya in a bit." Sans said towards Frisk as she was going to leave, until he had to pry his eyes away from her, and back to the two children who were literally tugging on his arms to try and get him to walk towards the line. "alright, alright, don't cause me to pop a socket." Sans chuckled, finally beginning to walk with Leo and Luna, as they joined the back of the line to see Santa. Luna was practically giddy, as she found it difficult to stand completely still, while Leo looked more curious, as he clung to his father's hand.

While this was happening, Frisk made her way through the mall, trying to find a good store to go into, to find some presents to buy for the kids. She also needed to buy other presents for some of the others... Geez, she was so crazily unorganised this year. Going into one of the stores, she glanced around, wondering what to buy. Luna really was a girly girl, seeing as she was only a 6 year old who was obsessed with princesses, so maybe she could buy her some princess-y dolls for Christmas. For Leo, it was so much harder to shop for him, cause with him being a quieter boy, it wasn't as easy to know what his interests were. He definitely took after Sans a lot - not that that was a bad thing. It just made shopping all the more difficult.

"Frisk?" A voice spoke up from behind her, causing the girl to turn around in wonder, only to be surprised as to who had been speaking to her. Chara! 

"Chara, what are you doing here?" Frisk questioned in surprise. After all, she would have figured Chara would have done all her shopping by now, not only that but this mall was pretty far from where she and Asriel lived. It seemed more worth it to shop in their area, than to come here. Chara's explanation would cause her confusion to disappear though.

"Well, I was coming to see you and Sans, but I wanted to do a little extra shopping first..." Chara mentioned. She wanted to buy a couple of things for Asriel, which was why he wasn't here with her at the moment. "I also wanted to mention to you that we're having a Christmas party in a couple of days, so I was wondering if you guys wanted to come." She mentioned. It had been awhile since Frisk or Sans had been to a Christmas party - a couple of years to be exact. Chara and Asriel had thrown a couple of Christmas parties over the years, but it had been awhile since they had thrown their last one. 

"I'm sure we'd love to." Frisk nodded, gladly accepting the invitation of getting to go to a Christmas party. After the last couple of hard weeks her and Sans had, interacting with everyone at a party sounded like it could be good fun. She would have to let Sans know once she was reunited back with him and their two kids after her little shopping spree, but for now she was going to spend the time with Chara, catching up a little as it felt like they hadn't talked nearly enough as they should lately. "How have you been anyway? Have you told Asriel how  you feel yet?"

"Not... Exactly." Chara sighed. "I didn't know it was this hard!" She grumbled, almost seeming like an angry child as she pouted and followed Frisk around the store. After all, Chara would never forget how she had been trying to help Frisk, and then Sans, when the two had major crushes on each other. She treated it like it was easy to just gain the courage to tell someone you cared about that you loved  them. But... It wasn't that easy. Any time she even thought of saying anything, she felt her adrenaline kick up to the point it made her way too overly anxious, and her mind began to kick into overdrive. Anything that she had practiced trying to say to Asriel went right out of her head, and she couldn't seem to remember what she wanted to say, so it all just would come out in a mess of gibberish, until she glumly muttered a "never mind", leaving the goat confused. 

"Why don't you confess to him at the party?" Frisk wondered, while Chara looked extremely unsure. If she couldn't even confess to him in a room when no one else was around but them, how the hell was she supposed to tell Asriel about her love for him with so many eyes and ears around. Frisk smiled. "Me and Sans could always help you." She suggested. She could treat it as a way to pay back for all the ways Chara tried to help her and Sans. The girl in the green sweater stared at Frisk, questioning how she would even help her, but Frisk already had an idea in mind. "Don't even worry about it, me and Sans will have you covered." Because there was one good thing that really could help a couple get together around Christmas time.

And that was mistletoe.