Though most tandems in the US are sold to paired adults or couples, over the years we’ve also built quite a few tandems for parent/child use. The tandem is a great way to keep everyone together, and to help young legs handle longer rides and more challenging terrain.
All 3 of our kids spent time on the back seats of our tandems; we had a lot of fun and it proved to be a great way for them to learn more of the subtleties of riding off-road. It also created some fun memories.
For very young children, yes, sometimes a trailer or child seat is better, and the trail-a-bikes are useful for casual riding, but when the kiddos get big enough to ride on the back seat, nothing performs better than a tandem for off-roading, touring, racing, or just cruising with kids!
So consider a tandem as a great way to share the many benefits and adventures that bicycling offers with your favorite little person!