I have a 3 year old goose that has been sitting on infertile/dead eggs for a couple of months. She proved last year to be an excellent mother last year. I just hatched 6 healthy ducklings last week. I have been told it would be okay to put the ducklings under mama goose seeing as she is broody & obviously waiting for some babies. My question is, how old should the ducklings be when I put them with her? Thank you.