We mainly used a trek 2 child trailer. I don't believe they make these any longer. What I most liked about the trailer was that it was basically 2 individual seats made out of a nylon type fabric. It was like it snuggled them in. I certainly appreciated that each child had their own space. Our double trailer had a weight limit of 100 pounds.Still used it with kids about 4 and 7 however had to consider the route I'd be riding. The Chariot 2 child is also nice, we used one of those a couple times and the kids were cozy. I would avoid any sort of trailer with a hard molded type seat. Sleeping kids equal a longer ride! Also check out the WeeHoo. We had a single one however they do make a double. My kids started on the WeeHoo at about 2.5. and rode up until about age 8.