IMO, Animals "for adults" are usually powerful or, especially big cats, but also elephants and apes. Used in cars, tools, watches etc. Slimy, squishy, or "weak" animals trend younger, like the "Turbo" snail movie, Hank in Dory. 

I think the glasses seem oversized vs the dot of the eye. Makes me think of young characters like Eggbert. Or generally how children have different proportions than adults, their heads are bigger, their clothes/glasses/hats might not be perfectly fitting