I do up a fee schedule twice a year, outlining the fees in 6 month increments. I do not do flat monthly rates. Each month is tallied by the number of days scheduled, multiplied by my daily rate, and due whether they attend or not. All my stats are paid, as well as 2 weeks of holidays are paid. I also take a 2 week non-refundable deposit to be applied to the last 2 weeks of care.
Post dated cheques are due all on the 1st of the month, or divided btwn the 1st and 15th. I take 6 months of post-dated cheques at a time, so I'm not hunting down parents for payment.