I charge slightly more during the Sept - June to compensate for the summer and then have a couple summer options depending on if they want the child to come 1-2 days a week etc.

Your hours of care, your overtime rate and what you base that on could be one issue. I know I signed a teacher on one time because she was finding people were basing care on her working hours and charging overtime from there. While school ends at a certain time and on most days she could come right after there were also days a parent calls at the last minute or she is asked to fill in on bus duty for another teacher. Because I based my rates on up to 10 hours even though she only normally used just under 9 she signed because I agreed not to charge her for the first 20 minutes past her normal time which was only 9 1/2 hours so well within by timeline.