As you mention the IRS will allow the expenses for the client’s child if they are claimed as a dependent on the client’s tax return and will typically not if the child is claimed as someone else’s dependent. If this were my client I would have my client see if the ex-spouse would allow the child to be claimed on the client’s return until the offer is pending (the client could reimburse the spouse for any tax savings he or she is foregoing). If the spouse is unwilling I would still include the child in the offer and use receipts, etc. to argue the point.