I'm Lucy, and I'd be happy to answer your questions today.
There really aren't any laws about what child support needs to cover, but the parent who receive support is expected to pay for the child's needs with it: food, shelter, child care, clothing, etc. Unless the court order says so, you do not have any obligation to give a penny over and above the child support. It's up to the parent receiving support to determine how best to use that money to make sure the child is taken care of. When a child has extraordinary expenses and child support isn't enough, then it's up to the parent receiving support to go back to court and ask the judge for an increase.
Extraordinary might expenses include things like unexpected, required medical expenses, extra-curricular activities, private school tuition, and things like that. If the mother is receiving the amount of support the law says she's entitled to, it's hard to imagine how she'd convince the judge that she needs extra money to buy clothes. If it's been several years since the support order was entered, you might want to look at this calculator to see if a judge would likely order an increase if you went back to court. That could help you negotiate an agreement (if any change is necessary).
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