Ken,
I have a fairly basic Garmin GPS 72 handheld that I use for the tracker system and for fishing. I haven't spent a lot of additional time trying to figure out the rest of it. Depending on the parks that you will be visiting, a lot of them are now posting way points on their web-sites/maps. With most of these hand-helds, you can enter a way point and the unit will direct you to it.
If you have not checked it out already, you need to look into geocaching (geo-cashing). Your boys will love it. It is a great way to check out different areas and a lot of fun. Check
http://www.geocaching.com/ Tim