When the twins were big enough to go along with it, I took one of those enclosed trailers for 1 or 2 kids and pulled them around in it.
Sometimes I wanted to pull all 3 kids somewhere, so I'd hook it all up together. Bikes + passengers were 450+ lbs. 5 wheels. Impossible to back up. Tight turns need extra clearance. It was certainly good for looks & comments of passers-by. I finally got a picture of the "full train" as I call it, to share with you, dear reader.
Reid got comfortable riding his own bike this spring. He was also getting so big that there was too much flex in the rig when going slowly up a big hill. It was time for him to graduate to riding on his own.
I wasn't sure if I should hold on to his tandem trailer for the 1.5yrs or so until the twins were ready, or sell it now & look for a replacement when the time comes. I don't know how I'd take both of them anyway, since two of these things bolted in tandem would be very unstable. I've seen a picture of one with two seats, for two kids. But I don't think they can be found in the US. Maybe I could get a kidback tandem and bolt a tandem trailer on to it. Maybe I'll learn to weld and build something custom. Who knows?
I decided to offer the tandem trailer as a loan to some friends, and at the same time, post it on Craigslist for a high price. I figured that if it sells at a high price, then I can use that money to buy whatever I decide I want when the time comes, and have less clutter in the meantime.
Sure enough, someone in town decided to buy it. So, it's gone for now.
If you're considering biking with kids, remember that flex will matter a lot. The extra weight of the load + the extra pedal force you put in trying to pull it will push your frame harder. If you have a cheap bike, or a racing bike, it'll suck. My touring bike is built stronger than average, and I still wanted more stiffness. If I was doing it over, I think I'd go with the Burley Piccolo, which connects to a rear rack, not the seat post. It's stiffer, and the tandem trailer leans properly in turns.