Some mons requires spending more money to choose their sex when u're breeding.
For ex. Abra, Timburr, Machop costs 9k to chose female.
Starters, Snorlax, Eevee, Fossils, Riolu, etc. costs 21k to chose female.
Babies = mons that need to lvl up to 30 to evolve and be able to breed.
Riolu = it's a mon that need to evolve for breed too. It requires lvl up with happiness+daytime.