I liked the intro, it made me laugh. I think it had a little bug though because the two music tracks overlapped at one point.
I think the pixel art for the baby and fishes is spot on, I like his little pacifier especially. The enemy attacks are a little tricky to read, I think the fishes could "wind up" somehow before lunging, maybe by wiggling their tail fin, to give the player a better chance to dodge out of the way.
I wish I had a brother to make games with. Like, I'm legitimately jealous. Have fun you two.