This scene reminds me of Chapter 10 Bittersweet Love. From my fanfiction: Harry's Little Dividend. It is a heartbreaking scene. The Chipmunks and Chipettes are down in the living room; while upstairs comes the agonizing scream of Vinny, who is going through a difficult labor. Brittany and her sisters weep for her. The boys and girls had just gone through a growth spurt. So this is how they would look like.
You're exactly right! I've always loved how Alvin is a jokester, but when it comes down to it he's always there for his family and friends, and he can be serious when he needs to be. If nothing else, he loves Dave, his brothers, and the Chipettes so much! He'd do anything to make sure they were safe!