There is a baby seat option for many of the various upright tagalongs, which replaces the saddle. Not only is it a big drag like a rack mounted baby seat, it also make it completely impossible for the child to try pedaling. My advice is to find a used Weehoo or look for the older steel model on clearance somewhere. For smaller kids that don't pedal much and can't be trusted not to hop off the bike in traffic, the Weehoo is night and day better than the various upright tagalongs.