Create a "pay for future charge" section where future charges can exist and be paid for but not charged on the account until the assigned date

Oftentimes parents pay early before their account is charged. So, since the charge wasn't applied yet, their account balance would be positive. This is great, however, there are some times when the parent may pay so much in advance for one thing, for example, private lessons, but they owe money for something else, for example, a costume. But, even though they owe money for something else, their account balance would still be positive because of the money they put in from a different payment. This tends to confuse many parents when I tell them that they owe money, but their account is showing a positive balance. I was wondering if there was a way to apply payments to future charges that are to come so that their account balance will always be accurate. This would be extremely helpful for me. My suggestion would be to create a section where future charges can be listed and the parents can apply payments to those. So when the charge IS posted, it would automatically be marked as paid.