See my thread. I am in the same boat with our 2 year old
http://www.bikeforums.net/showthread.php?t=561546
The trailer is the Schwinn Spirit, we picked it up at our local big box store for 150 and the little guy loves it. we got the bikes from a friend that had them cluttering his garage for very little. we actually dropped them off at the local bike shop to get the brakes and cables swapped out. (total or $100 each for parts and labor) but it is worth having them give it a once over since we are hauling valuable cargo. our first real ride I ate the rear brakes trying to keep the trailer at a reasonable speed on the down hills.
be sure you are in decent shape its alot of work to get that trailer moving but once you get it going you hardly notice it unless climbing a very steep hill....
we have had our bikes for about 2 weeks and could not be happier. they are big box store bikes but have been well taken care of and other than sitting for 5 years had no issues with them... the gear cables had stretched and the brake pads were a little dry rotted. expect to swap the cables and brakes almost immediately. my rear cable had stretched far enough to be pretty much unusable in the first 2 days. then after a couple of good down hill rides at our local green ways the rear brakes were flaking off like deodorant.
just some expenses to concider based on my experiances.
our totals were:
mens bike $40
ladies bike $40
trailer $150
helmets about $50 for mine and hers on sale at local sporting goods store
(little man should not need a helmet in the trailer, the roll cage means he cannot touch the ground)
mens bike parts and labor for all cables and brakes to be replaced $100
ladies bike parts and labor for all cables and brakes to be replaced $100
Gatorade $$$$
Amount of fun we are having = priceless....
we love having picnics at the park with the trailer... there is lots of room in the back for storage.
it folds down to basically the size of the box 2' x 2' x 6 "
its a great little trailer for the money.
also it converts to a stroller if you want to go walk with it. (all parts included)