As rainbowchaser said the end of July is a bit tough for dry fly fishing except terrestrials, and right before&after dark is better for fishing, so the dry fly fishing will be tough. But daytime nymph fishing is still pretty good here in late July. Work mostly the riffles and faster runs as the water will be more oxygenated as well as cooler in the riffles. Also work the areas around feeder streams that dump into the river.

Basic rig with strike indicator/small shot and hares ear or BHPT nymph will take trout in the runs.

For the family day trip info Penrods http://www.penrodscanoe.com/ is one of the main canoe rentals in Gralying, or for the mid section (Mio) Gotts http://www.gottslanding.com/ is a big one, or lower river Alcona canoe is the main one http://www.alconacanoes.com/

There's some good size sand dunes at Lumberman's monument where your boy can climb down the dune to the river for some fun. Going down is easy, going back up will kill guys over 30 yrs old lol.
http://www.michigan.org/Property/Detail.aspx?p=G20389

Steve