I steered clear when they were that age.
We did tours with one on the tandem and one mainly sleeping age nearly 2/nearly 3 in the kiddy seat.
Then I went with a nearly 9 and nearly 12yo a couple of years ago, to Holland (yes I do mean Holland), probably about 30 miles/day with a rest every 2-3 days to be tourists.
It was fine.
The main thing is to break it up so they don't notice - ice creams, parks, meals, beach and back ...