In my contract I state that each month's fees are due on the first of each month. I charge a daily rate so each month's fees are usually different. A few days before the 1st I send an email to each family to let them know the total and any additional fees and show a breakdown like this ($50 per day x 20 days + $15 for early drop off on Dec. 1 = $1015 total). I know they can figure it out for themselves but if I send the breakdown it is there clear as day and then we don't have any problems with "forgetting" anything. If I end up closing and don't charge for a day whatever difference is made up in the next month's fees.
I find that parents like it to be clear.
If they forget the cheque in the morning I remind them to bring it at pick up time.
So far I haven't had any problems.
Good luck!