This park was GREAT before we had children. Lots of nice hiking trails (not very stroller friendly - even for the jogging strollers with big wheels) and decent fishing. It was much easier to avoid the swimmers itch and biting flies at the swimming beach before we had children. Our son contracted Lyme disease from a tick bite he received here in the summer of 2008 - so watch for those.
Children catch a bunch of panfish at the campground dock - but be careful - the dock is small and there are no railings. Another nice and much larger dock is up the hill and it has railings, but infants could crawl through in places.
Fun geocache location too - but again, it was a struggle with our hiking stroller and we may as well have carried the toddler and infant.
**Don't forget to stop in the nearby town, Pelican Rapids, and take a picture at the giant Pelican, play in the playground and/or swim in the city pool, and get ice cream at the ice cream shop - it's DELICIOUS and they have a back courtyard eating area where little ones can roam free without worries of traffic