My only suggestion would be to make the backgrounds bigger, and you can do this by just zooming them in double their current size. The babies will look even smaller, which I think would be a good thing since they're supposed to be teeny! And the adults won't look so big. Maybe make the grass near the front more defined and bigger, to make it look like there's more of a foreground and to give perspective.
Hope you don't mind I edited your artwork. Figured a picture to accompany would show better what I mean.
Edit: Even if you don't make the bg larger, I think just adding some larger defined grass like I mentioned will give more size perspective.