Our DD is 5 yrs old. We started when she was 3. A must for us was having enough space in the TT that we didn't trip over her or the dog on a rainy day. We have toys, books and stuffed animals that stay permanently in the TT so that she doesn't tire of them. We keep a soccer ball and small net, corn hole, bubbles and a few other odds and ends for her to do outside but on a rainy day nothing beats galoshes and a raincoat for stomping in mud puddles. Family bike rides are a lot of fun and the trail gator device (http://www.trail-gator.com/
) is great for hooking her bike to mine when she tires. I try to make sure the majority of campgrounds we visit have nice playgrounds for her and in the summer, somewhere to swim is key. We also look for campgrounds with planned kids activities but a state park is good for a nature lesson or two. She likes to help with sweeping and setting up for dinner but roasting marshmallows is a favorite. We also keep movies in the TT for rainy evenings.
I was worried about her falling out of her bunk early on but the opening for the bunks in our TT was too small for a bed rail. We took the cushions off the dinette and placed them on the floor so falling out of the bottom bunk wouldn't hurt. The bunk space is difficult to light with a nightlight so we put glow in the dark moon and star stickers in there for DD. made it a lot less scary for her.
Watch the little ones close, I was messing around in a cabinet organizing something and DH had taken the trash out when DD decided to take herself for a walk. She made it 2-3 campsites down the lane before we could get her. Some will use baby gates to lock the door, we just trained her out of it. You can also put a piece of plexiglass on the bottom part of the screen door so little ones don't push through the screen door. I have heard some mention folding down the dinette and placing pack and plays there for little little ones to sleep.
For traveling, the portable DVD player and ipad nabi (iPad designed for kids w/kid safe web pages, games etc) have been lifesavers. She has headphones so what she is doing isn't annoying or distracting. We also have a travel game of bingo that has us hunt for things on the trip (ie cows, plane, etc). I also loaded kids games on my droid.
We have learned to plan in a stop every 2 hrs and limit liquids to prevent potty accidents. Be ready to hit the shoulder at any time or know what is coming up at the next exit for potty breaks. We also keep snacks readily available. Be aware eating meals in the car doesn't work so well when they are that small so if the trip warrants we plan a longer break in to eat lunch in the TT at a rest stop or truck stop or somewhere of the like. This stop is a good place to get some energy out. If you have a pet, have her come along on the potty walk. If raining, wander inside the shop at the truck stop and talk about the interesting things you find. Try to plan trips during nap time to get them to sleep some of the time. The one in the passenger seat is responsible for keeping DD occupied while the driver focuses on towing the 30' monster behind us.
During set up, take down, hooking up, leveling, slides going in and out etc DD knows she must stay in TV, TT or on the picnic table. We both watch for her, but one takes responsibility during these tasks. DD also thinks sitting on the sofa while the slide moves is a fun ride. Hope this helps other parents.
Ps first trip out DD locked the door to the bathroom with no one in it. Took us about an hour to disassemble the door handle to get back in. Then DH had to reassemble it. You may want to switch the door handle to one with no lock on it.