My kids love being on the bike. Ages 7 and 9. We've done Madsen Bucket, Xtracycle, several different tandems. cheap trail-a-bike, expensive trail-a-bike (Burley)...
Never toured, though. I think that a Tandem with a kidback makes the most sense. There is also a large difference in weight and stability between the WeeRide and Burley trailabikes.
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The bicycle, the bicycle surely, should always be the vehicle of novelists and poets. Christopher Morley