I've got a 1.5 year old son who loves being pulled around in the Burley trailer. We can get a good 10 miles in before he needs to get out and start running around. (But if we stop at a park mid-ride, then I can't get him back in the trailer!) Even with a short ride, Daddy still gets a workout because of all the weight he's pulling up hills - even passing some other riders uphill on occasion!
I usually do a ride leaving from the house, since the extra time being strapped in the car seat limits our riding time when driving somewhere for a remote ride. Or if I think he'll still be happy after a drive, we'll drive down to the Newport Back Bay and do a ride there, along with a little out-and-back on the San Diego Creek trail.
Anyone else pull their little one in a trailer?