I have tried numerous biking con toddler options. I have a mountain bike, and at 2 and 3 (their big kids) my kids were getting too big for the rear-type bike seats, although there are some models with a higher weight rating that the type I had. I just bought a Chariot Cheetah stroller/bike trailer and I really like it. Down side is that I had to save for months to buy it, lol. My son really liked the front-mounting seats like Weeride, but it wasn't as comfortable for me to ride with as the rear mounting type.
Good luck, it's so fun to take the kiddos for a ride!