The July '02 issue of Bicycling magazine had a very brief review of 8 child trailers. Although that's 8 years ago, I'm sure the field of child trailers doesn't change very quickly, so this may still have some value as a starting point.
The four top ones were the
Yakima Caddy Yak (five-chainring rating, $425, yakima.com),
Burley D'Lite (4.5 chainrings, $429, burley.com),
Wike Moonlite (4.5 chainrings, $269, wicycle.com), and
Chariot Cougar 2 (3.5 chainrings, $400, chariotcarriers.com), in that order.
The four bottom ones, all of which tipped over more easily according to the comments, were the
Trek Transit Deluxe ($449),
Instep Turbo Elite ($300),
Cycletote ($455), and
Kool-Stop Papoose Caboose (only a two-chainring rating, and costing $295).
Of the top four, all having 20" wheels and easy or very easy assembly:
Yakima: 27.5 pounds, aluminum frame, chainstay hitch, 25"-wide seat, $100 stroller kit. Harness has nice chest patch for comfort; good leg room; big side windows; safety light.
Burley: 20.25 pounds, aluminum frame, chainstay hitch, 20"-wide seat, $99 stroller kit. Sliding mesh pockets for easy toy access; good visibility and ventilation; curved frame sides give kids elbow room.
Wike Moonlite: 22.5 pounds, aluminum and chrom-moly frame, skewer hitch, 22"-wide seat, hitch reverses to stroller arm. Easiest to assemble and convert to stroller; big windows, lots of leg room; noisy plastic floor, smallish cargo space, separate from kid area; includes two bike hitches.
Chariot: 25.5 pounds, aluminum frame, skewer hitch, 21"-wide seat, $40 stroller kit. Sporty, compact look; separate cargo space with external pockets; adjustable suspension; tracking a little jerky; accommodates children under one year as stroller.
Also, what is the earliest age you can put a child in a trailer?
I believe they're supposed to be able to hold their head up with a helmet on.