Here's some thoughts and research on how we could take the adorableness of bighorn lambs and translate it into a cartoony design aesthetic.
To start, here are a couple photos of bighorn lambs:
The main notes for adorableness here are pretty much the same as what Chris said in his earlier post. Bighorn lambs have a bony, flimsy looking build, large shiny black eyes, cute little noses, etc, which make you want to protect them.
Now for cute things in animation:
Archie the scare pig has these flimsy little legs that make him look frail but still playful - a trait that can be seen in the bighorn lambs above.
One thing I really like about Mavis from Hotel Transylvania here is how simplified her shapes are.
And lastly, Puss in Boots has ridiculously big, overly shiny eyes that help to communicate a sense of over the top cuteness.