Child support is the obligation of ever parent. Under the current version of the Illinois child support statute, each parent has to provide child support, but what is not included in child support? Here are some generalized guidelines, not to be applied to your specific case, only meant to educate generally.
Typically, health insurance premiums for the child are not included in child support in Illinois. If you provide health insurance for your children, you would calculate how much coverage would cost just for you and subtract that from coverage for you and the children. The difference is the obligation of both parents.
Health expenses for the child that are not covered by insurance are not included in child support. Typically, these expenses have to be for in-network providers and for necessary treatments, not elective. Some examples are co-pays and out-of-pocket payments for prescriptions.
Required school fees and uniforms are generally outside of child support. This is typically limited to public school registration, lab and field trip fees, and uniforms required by the public school.
Agreed upon extracurricular activity costs are usually not included in child support. If the parties agree that their daughter participate in organized ice-skating, they typically have to contribute to that cost.
Any other agreed upon expenses or ones determined by the court to be in the child's best interest, despite lack of agreement. For example, if a son was a stellar hockey player in expensive travel hockey, which looked likely to lead to a university scholarship, a Judge might order the parties to a divorce to continue paying for the activity despite a parent wanting to withdraw his/her consent, assuming they can afford it. A Judge can also require the parties to contribute to private school expenses in certain situations.
Of course, after a child's emancipation, child support stops and do most of the obligations to contribute to the child's expenses, but then another law requires contributions to college expenses.