The Wonder Weeks - that tells you all about their leaps, when they’re about to get fussy and the new skills they’ve learned/learning in that stage. Obv all babies are different, but if our LO has hit any skills ‘late’ then I’ve just gone back and ticked them off that way xx
Google, pampers had one, and a few other random good ones (not apps), I still check monthly where my little one is and they pretty good
Start for life (not an app) or Emma's diary
Glow baby!
My first five years