We have spent years camping in Turner Falls! We Love it! The best part, though it may be a bit cold now, is that most of the river is only about 4-5 inches deep and its mostly a solid rock bottom. I put swim shoes on the kiddos to give them traction bc it is VERY slipery and they run up and down the river all day! But since it is spring fed, Its very cold water. You can go to the bottom of the river and there is an actual swimming area, one with a beach and one that is rock w diving boards and such. Up on the top part of the river there are various little swimming holes that may be 3-4 feet deep. All in all, its a very kid friendly place, we have been going since my 15 year old was about 2. Ther is a bath house for hot showers and a littl cafe type walk up restaurant at the entrance.
Have a great time!