creature spawn and something like a baby mob

hello, I created a creature called "Gerbil" and I want it to be able to reproduce with seeds like a chicken but that the same mob comes out, that is, I don't want a Babymob.
If possible I would like you to send images to understand well, thank you!
(In case they are good, also explain to me how to make the same mob come out when pressing the egg spawn)
These are basic things that every normal minecraft creature should have and I want it to look like that.
I hope for your help and sorry if something is wrong written since everything is the translator's fault hahaha