I already had the seat on the front part of my bike for Annabelle, but I recently added the seat on the back too so that I can take both kids out riding. The plan is to ultimately take Belle to school this way so that I can get some regular exercise in. The school is only about 5 miles round-trip, but with 50 extra pounds and compared to the exercise that I get now, that's not too bad. We also need to get an extra rack for Keith's bike so that when we all go riding as a family, he can ride with the back seat on his bike instead of me having both of them.
Check out my sweet ride, my bicycle built for three. :)