And yes, the original benefit per child is up to 1/2 of the parent's Primary Insurance Amount (PIA), but it is subject to the Family Maximum (FMAX) which can equal the PIA, in some cases. It is a complicated formula. The FMAX is like a pizza or apple pie. If you divide it by two, each person gets 1/2. If you divide it by 3, or 4, or 5, each auxiliary gets a proportional share, less than 1/2 per person. When your oldest child turns 18, benefits will increase for the two remaining. But when the second child turns 18, the benefit for the remaining child will remain the same.