Orange Yepp Maxi child bike seat attachment. Adapter also available. 

This thing is amazing!  Super secure and plenty of room between rider and child. In great used condition.

https://www.thule.com/en-us/child-bike-seats/rear-mounted-child-bike-seats/thule-yepp-maxi-_-12020234

$40. Highland Park pickup. Photos available on request. 

- Tamar