Cool!
A baby donkey is a jack if it is a boy, jennet if it is a girl, jack is also a mature male and jenny is a mature female.
A female donkey/male horse foal is a hinney. It is harder to get a hinney than a mule. It is very rare to have a stallion that will breed a jenny and even more rare to get one to settle a jenny. The chromozome count is different between donkeys and horses. That is also why a hybrid is sterile (at least 97% of the time. there are VERY RARE occasions)
A male donkey/female horse foal is a mule. You have to have a special donkey and mare to actually get a mule. Not all jacks will breed a mare and not all mares will allow a donkey to breed them.
Some say the hinney has a prettier face than a mule but I'm not sure about that. All my mules have beautiful heads/faces.
A gelded jack is a gelding.