Dark Author asked me if I had updated this booster seat that he'd found posted Click Here on Inseminator.
I have made changes to the mesh and files.
It's found with the other child items for $35
To place it on a chair the chair should have already been placed at a dining table, otherwise, the booster seat won't line up right. You can actually place the booster seat pretty much anywhere, but I positioned it to work on a dining chair.
No cheats are required to place it on the dining chairs either.