Another Late Rent/Fee Question

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Lease states a $25 late fee if not paid by the 5th of the month. Last month a young couple with 2 month old baby paid late. Very late. I was lenient. Why? Because on a hunch I looked at public records and saw that the young girl filed for child support against the father. I gave her a time line with payments and she got caught up.

This month? Nothing. The father is still living with her. Not sure what the deal is. Anyways, I am charging a late fee this month, but, do I send a notice? What's the protocol? 

Thanks!