Yes, yes, yes, get tough now! Make a bill for them stating all the late dates and start charging a late fee when payment isn't received on time. Make a letter to all of your clients 'just as a reminder of the rules' so that you aren't centering anybody out if it makes you feel more comfortable, but the people who are causing the problem will know who they are. When it comes to my contract rules I'm a tyrant. You have to be a tough businesswoman with the parents and a caregiver for the children, 50/50.