If a male with a blood type of AB mated with a female of the O. What would be the children's blood types?

The Children would have a 50% chance of being type A and a 50% chance of being type B

The ABO bloodtyping system classifies antigens found on blood cell surfaces into three families: A, B, and O.

The alleles for A and B are dominant; the allele that codes for Type O is recessive.

So, if the parents were AB and OO, first generation offspring could be: AO, AO, BO, BO. Since O is recessive, there is a 1:2 chance offspring will be Type A, and a 1:2 chance they will be Type B.