CrocsKids' Classic Marbled Tie-Dye Clog

My daughters current croca say size J2 so would that be a little kid size 2? Im confused by the sizing shes 16 but has very small feet.

Big kid size 4 is too big for me, what size should I get?

I am told that uk size 3 is equivalent to u.s. size 4. would that be size "4 big kid" ? kindly guide. thank you

Would these fit my 9month old? He uses size 2 and some 3. Yes or no ?