Suggestions on touring with a 5 year old?
We did ~100 mls with our daughter last year in Quebec when she was 6, over a few days. Her on a Gary Fisher tag-along attached to my LHT or my wife's road bike. You will need to take it as it goes. She'd want to stop for anything from a veg stand, to a playground, or a hiking trail. One day, she didn't want to go on the bike at all. So we walked and hiked.
In general, the faster I'd go, the harder she'd pedal. But I wouldn't have expected to do any more than 25 miles in any given day. Before that, we had done plenty of ~20 mls round trips to the next town, and even a 25mls Sunday ride with a local club. So don't expect to take off like this without trying first.
Oh, and one thing: get your kid some padded bike shorts and even a suspension seat post. I even lowered the pressure on the trail-bike a little.
Good luck, it's all fun!