Sans: He would tilt his head, looking at the drawing, then laughs shaking his head "Y/n, come on, I knew I drew the short stick in my artistic level but you don't gotta hide your stuff to make me feel better about it" he ruffles your hair. He thinks that the drawing is amazing, and you should be proud of yourself.

Blueberry: When he sees it, his eye sockets widen, then he grins all excited "Y/n! This is amazing!" he holds it up "Why would you ever think that this is bad? It seems extraordinary to me!" He can't believe that you would ever think your art is bad! He wants to put it on the fridge. Can he, please?

Demur: He gets not thinking that your stuff is any good... if you really don't want to show, he wouldn't force you. When you do show him, he tilts his head to look at it "Oh..." he mumbles, then leans against you a little, messing with the scarf around his neck. "I think it looks really nice, Y/n... you should be more proud of what you've made" kinda ironic coming from him but eh, whatever.

Red: He looks at the picture, and makes a soft tsh sound, turning his head away feeling embarrassed about his, shitty compared to yours, drawing "Oh shut up, Y/n. Yours is good..." he's annoyed that you don't see that you're good at drawing. 

Axe: He looks at the picture, turning his head to the side, then the other. He smiles and reaches up, patting the top of your head "Good" He bonks his skull against yours gently, then takes the picture and folds it up to put into his pocket. He's keeping this. He thinks it's a really good drawing, and he doesn't want you to try to erase it or throw it away.