There is a difference between a late fee and an interest charge, so it's possible for a late fee to accrue in amounts that would not be proper if they were charged as interest. However... late fees are contractual. They can only be charged if they are part of the agreement between the business and customer. The first place to look is thus the contract for daycare services, to determine if in fact late fees are authorized, in what amount and with what frequency. Late fees are also subject to a test of reasonableness, but what's reasonable in one state (or under one set of circumstances) may not pass muster in another. It's possible for an inartfully drafted late fee provision to be regarded as a court as interest, in which case usury laws could be applied, but I wouldn't assume that to be the case. See the discussion in BMG Direct Mktg. v. Peake, 178 S.W.3d 763, 775 (Tex.2005) .

Not that I think it's relevant, as I doubt that the daycare is either incorporated in Delaware or that the contract would be governed by Delaware law, but Delaware does have a usury law that limits what its companies can charge. ("Any lender may charge and collect from a borrower interest at any rate agreed upon in writing not in excess of 5% over the Federal Reserve discount rate including any surcharge thereon." 6 Del C., Sec. 2301).