Transactions assigned to parent account not student account

It would be great if transactions could live on parent accounts and charges made for student tuition be assigned to the parent rather than to the individual child. A parent who has $155 credit on one child's account enrolled her second child this evening and instead of the credit being deducted from the amount owing for child 2, she was charged child 2 fees of almost $200 in full! It's not the first time this has occurred and it is very frustrating.