I've researched and researched and still can't figure out which trailer bike to buy for my smallish 4 year old son. In my area, no one rents them, so this is a big leap of faith! Is size and weight an issue between the Adams, Trek or In-Step? Some of the handlebars look very high and far away from the pedals? Some manufacturers age guidlines are from 2 1/2 - 6 (Adams), and 6-9 (Trek) for their starter bikes. Are these very different animals? Although the In-Step's hitch is not the best, it looks smaller than the others. Also what happens when the child pedals? Must he pedal at the same rate as the person in front? Since the wheels are smaller, must he pedal faster?