We bought a new property a while back and just recently got it refenced so we could move the horses.
So 5 of my horses are now running together.. anyway, my 3yr old filly is in season and was winking at my 11month old colt Nullah, now I was under the impression they may show interest but wouldn't really do anything yet and if they did it wouldn't cause pregnancy(maybe I was being naive?!) anyway, he ended up trying to mount her so I promptly ended that and they are now seperated.
So to sum things up.. can they make babies? ;)
EDIT: Just wanted to add that a foal is not the goal here as I already have a stallion I would like to use for the cremello filly later on and he is certainly not it!