I think it is up to ten per wife.
if your willing to do the math you can multiply that number of maximum children per wife by how many towns that you can buy a house in.
(the amount of towns depends on if you are evil or good)
also if you move or change houses you gain the ability to get another kid
110 children, wow. Bowerstone Market:11 Bowerstone Old Town:11 Fairfax Gardens:11 Bower Lake:11 Brightwood:11 Oakfield:11 Serenity Farm:11 Westcliff:11 Bloodstone:11 Bowerstone Cemetary:11