S.G.
I used both the seat on the back of the bike and the bike trailer. They wore a helmet for both. The seat on the back was good for short rides, but I liked the trailer for long rides to the park as I could bring a picnic lunch etc. I still use the bike trailer (without kids in it) when we are all riding to the park for a picnic, or to carry chairs to watch fireworks or to carry soccer equipment to games. I have even used it for grocery shopping.