Evening cyclists
Quick intro: we're a car-free family and cycle for utility mostly (commuting, shopping, nursery run, visiting family etc), although do some "leisure" rides too. Have DS who is 2.5 and DD who is 10 weeks. I've cycled throughout both pregnancies and been back riding daily for a couple of weeks now. I've clocked up 20 miles so far this week, with the trailer and kids in tow, hoping it'll help get the baby weight shifting.
I ride a cheapish Trek hybrid, with mounts for kid seats both up front (Bobike mini) and rear (Hamax sleepy), and a trailer hitch (Croozer for 2, with an infant insert for DD). So in theory I could transport 4 kids at once, although I haven't tried it yet....! Using the trailer mostly at the mo, as DD is way too little to sit up in a seat.
We live in London (zone 2) and I don't find it a problem at all in traffic, everyone gives you tons of room (although I do mostly back streets so they aren't sitting in the trailer inhaling loads of exhaust fumes).
Merly - I'd definitely go for a trailer - but don't rely on it to improve your balance - the hitch means your bike can tip right over without affecting the trailer. definitely agree with getting the training if possible.