The hitch is semi-permanently attached to the seat post - you can get
them separately if you have more than one bike you want to use with
the TaB. There's a socket on the end of the trail-a-bike that slips
over that part, then a spring pin goes through to secure it. It's a
matter of seconds to connect it each time. I lost or had stolen
several of the pins over the years, but my bike shop gave me a
replacement one, and I was able to find them at a hardware store
later.

Two options that aren't talked about much are a mirror for the
parent's bike and fenders for both.

Is a 4 year old child too young for the Trail A Bike?

thanks.