According to the National Park Foundation:
I would highly recommend this to anyone with kids 4-12! Malachi loved becoming a Junior Ranger. The booklet was $3 at Yellowstone and totally worth it!
First - go to any visitor center and pick up you Junior Ranger workbook. One of the REAL Park Rangers with go over the process with you and your child along with the rules of the park.
Second - Figure out how many activities your child has to complete in the workbook for their age level. Malachi was in the youngest age category, so he had to complete 6 pages. We actually ended up completing 8 and we might work on a few more - or maybe we'll just pick up a new one next time!
Third - Attend a Ranger-led program. This was the hardest part for us. We kept planning on attending a certain program and then something would prevent us from getting there on time (brother with a blow-out diaper, cool animals on the side of the road, traffic, etc) We finally ended up hearing a talk on Grizzly Bears and their Habitat by Ranger Rick (not the raccoon =) at the Junior Ranger Station on our last day. We made a special trip into the park just to attend!!!
Fourth - Walk a trail or boardwalk
Fifth - Find the visitor center again and have a Park Ranger look over your booklet. After that they have your child hold up their right hand and "swear them in". Then they receive a patch!
They also have a bunco of Junior Ranger accessories you can buy, a vest, hat, binoculars, etc. Lots of it actually. Malachi ended up going home with a stainless steel collapsible cup, a whistle and some binos (just like Daddy's). I am seriously considering a vest, just so I have a place to keep the patches!
Craters of the Moon also had a Junior Ranger program. It was much simpler and the booklet was free because it's a smaller park, but we had a lot of fun with it. They actually become "Lunar Park Ranger's". Same process applied: walk a trail, do some activities from the workbook, attend a program and get sworn in. Malachi chose to wear an astronaut helmet for his swearing in and it was a little big!
All that to say - check out the Junior Ranger programs at the National Parks that you visit in the future. I heard several people say that they have a bunch of adults who ask to do the programs, just because they are informative! The Park Ranger who did our Ranger-led program at Craters of the Moon told me she always picks up a workbook and does it when she goes to a new park - and she's already a Ranger!
Go here to find a list of National Parks with Junior Ranger Programs and have fun exploring!