I charge a minimum fee for before school of £10 and after school £20, during the day, my minimum fee is £30 for 4 hours.
I find picking up from school with 3 x 18month old in tow, quite strenuous and disruptive for little ones sleeps. I will do it, but prefer not to, so only offer the service to children who have been with me since babyhood, or from the same independent school as a long term mindie.