She has always been like this. She is not bony and she is pretty alert. I have also noticed she is always licking/ biting at her paws (front and back) and she is always stretching out her legs. She does not limp when she does move, and doesn't act like she is in any pain tho. I have been keeping a close eye on her and will start weighing her daily as well.
And your kits are adorable in that video