You might be able to stand it, but can your boy stand it? I don't know which seat you are considering, but the bobike doesn't have much head support. My 1 year old falls asleep in the seat after 15-20 minutes. And when she does fall asleep, I either have to pull over and let her sleep on the grass near the side of the road for a while, or use my elbows to cradle her head while I limp along at 5 miles an hour.

If you plan to take longish rides, perhaps a trailer is the better option. That way your kids can fall asleep and still be comfortable. Keep the front mounted seat for shorter trips.