I'm looking for a solution to transport my 9 years old.
I find the Bobike junior : https://bobike.com/en/product/detail/classic-junior, no need of back carrier
Or the Polisport Guppy : https://www.polisport.com/en/bicycle/child-bike-seats/carrier-mounting-system/guppy-junior-child-bike-seat-white-for-kids-up-to-35kg_p782.html?id=594&cat=582&pc=1
This one need a strong back carrier able to carry 35kg. Someone know of a carrier which can feat with the disk break?