My dd (5, in year 1) has always been a "joiner". She is very active and energetic, loves doing organised activities, and can't seem to get enough of them - though I should add that she is very capable of entertaining herself happily at home for hours on end too. 
At present, she does Rainbows on a Tuesday and Dance/Acrobatics on a Saturday (2 classes). In school, she is learning the recorder and she is the school council rep for her class. She also spends about ten minutes a day with her dad, learning to read/write in her second language (her choice, not his!) That's all fine.
She is now very eager to add swimming, karate and gymnastics to her regime. Swimming would be on a Saturday morning before dance, karate on a Sunday and gymnastics on a Friday evening. I have told her that she can only choose two out of these three, because I am worried that she will overload herself. She says that she wants to do swimming and karate, but she is really disappointed about the gymnastics.
Am I being mean in not letting her go? It isn't an issue of cost or logistics etc, merely that I think she needs some free time at her age just to "be"! Or do you think I I letting her do too much already? I know that these things depend on the child etc, but would like to know what other parents think is a reasonable amount of extra-curricular activity for a five-year-old child!