help! need seat for older child on rad city 4

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Has anyone been able to rig a rear seat on Rad City 4 for a child. 6 years old, skinny. He has outgrown the burley trailer. Need a seat with spoke shield and foot pegs. I know rad does not make this for my bike but want to know if anyone has found an suitable seat elsewhere. Please help if you can. We ride to the beach together.