https://www.amazon.com/SANMERSEN-Bicycle-Footrest-Handrail-Accessories/dp/B01LPS75SU/ref=sr_1_6?dchild=1&keywords=bike+rack+seat&qid=1607715507&sr=8-6

I don't know how old your kid is. But my 6 year old nephew rides on the back of my bike no problem with this. I often switch out the seat for a saddle bag, so it is easy to get on off. I leave his handlebars on, as well as the foot pegs.

Bike with seat

Bike with bags