Serious comment - get some solo trike experience before a tandem trike - I think you have realised that.
Years ago, when I sold a TT, I refused to sell it to a couple who thought it would be good to put a kiddy seat in the back to take little Cloe out. They had no trike experience, no concept of how to handle it, just the usual silly notion of "it has to be easy and you cannot fall off".