In the beginning, they are babies. They're 3 and each one of them is different.
Omututchi, Mimifuwatchi, && Futabatchi
Omututchi= Cheerful Baby
Mimifuwatchi = Smart Baby
Fubatchi = Easy Going Baby
Normally, Mimifuwatchi (if male) Will end up as a Mametchi, if you train it's bond to 80-100% (You can do so by training it at 10:00, 12:00 AM, 2:00, 4:00, && 6:00 PM
Though the two oldest children will end up as the same group (cheerful, smart, or easy going) It's all the training you give.
1st item is to increase smart
2st item is to increase cheerful
3rd item is to increase easy going
Choosing the item will train it to -insert type- and possibly changing it to a different type from what it was in the beginning
Anyways, that's how I got Mametchi