I am finding my flyer babies a bit hit and miss anyway. I have four and sometimes only one will give me coal. Other times two will give me 2 each. I've been chopping lots of rocks. At least you don't have to wait for those.
On the Percival issue. I left the second baby in the forge until Percival was completed, and collecting from him for the biscuit.
Then I went back to the forge, put the baby into storage, then placed him on the board. So I have Percival and a baby bunny.
I'm happy with that.