How near to Munich do you want to be? We stayed in a lovely family campsite in Augsburg, which is 70km by motorway NE of Muniich. I reviewed it here:
http://www.ukcampsite.co.uk/sites/reviews.asp?revid=10161
This site has a really nice lake for swimming. The owners provide pedal boats, canoes etc. free of charge for the campers use. They also have a variety of go-karts, scooters, etc for the children to use, also free of charge. There is a tramplolene and a very good childrens playground. There's a nice little bar/ restaurant overlooking the lake.
The owners are very friendly and we found a lovely atmosphere here in general. The children immediately made friends here.
There's lots to see around here. We obviously liked it here - I would recommend it!
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.