When looking at child bike seats that are frame mounted, these seats use a bracket to attach to the frame of the bike. They have an extra bar that supports the seat and adds suspension to your child’s bike seat so they can move with you and they have no tension. Rack mounted bike seats use a carrier adapter and attach to your preexisting luggage carrier on the back of your bike. Both have there advantages and disadvantages but the frame mounted bike seat will give your child extra support and will be attached directly to the frame.