I saw one mom this year with a boy about 6. She also had a burley labeled "Jake's sag wagon" that she put him and his bike on. One crew was Grandpa, Dad, & oldest son on a tandem with a tag along all three towing a Burley with son2 & son3.
My boys (8 & 12) joined us for the two easy days.
That said, I'd recommend trying some long days well in advance. Kids have different physiology than adults and are more likely to get dehydrated or overheat. They are also not as hung up on doing the thing for its own sake - more likely to want to stop when it stops being fun. Keep in mind that if it is miserable you'll have lost them. That's why we decided to ease into it.
But if you do, look for us. You can tell by the Johnny Cash and Thai pop music