Both of our kids grew up in a Winchester double wide trailer until they could fit a trailer-bike. There was one awkward year before the first was big enough for a trailer-bike and the baby was occupying the full Winchester in a suspended car seat. That mean each of us towing a Winchester. Two bikes, two trailers, two kids. We only did short rides that year since we could not change out the tractors.
The trailer-bike attached to the seat post. I could still carry panniers, but the top deck was lost.
The trailer-bike was used. Don't know the brand. Rock doggone solid and with the stoker, a pleasure to pull.