Sounds to me like Blackcat's approach may work well for you. That mom picking up later than she used to may work really hard to commit to earlier pick up if it costs her less. Money always talks. I personally did contracted hours where the contract specified the start and stop time for each family. That way, other people's pick up times didn't affect each other. I base the fee on how many hours were contracted. Being late was defined as the time on the signed contract.

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