I commute everywhere here with the girls on a bike with me, the way many moms do in Japan. The commuting bikes used here are called "mamachari" and they have child seats on the front and the back, so that you can put a baby or toddler in the front basket while your older child rides in back. There's a steep learning curve when you are commuting with two kids, as the bike is pretty heavy (I'll have to take a photo one day), but it's a lot easier to navigate the narrow streets here on that than in a car.
Anyway, M really wanted to put a bike seat on the back of her own bike so she could pretend to do what I do, so we whipped one up pretty quickly. Here are basic instructions. We made it plain, because there just wasn't a lot of time to decorate, but you or your child can do whatever you want to spiff it up!
All you need are two pieces of rectangular cardboard, around 11 x 14 inches or so.
Fold one near the middle (I think I folded mine about 2/5s of the way down), and then use scissors to cut about two inches in on either side.
Fold up the sides
Fold it over as shown in the photo, and use staples or tape to secure.
To attach it to your child's bike, take the other piece of cardboard, fold it into thirds and tape it so that it's firm, and then attach this piece to the bottom of the seat you just made. Then tape the other end to the bottom of the bike's real seat. (I had to tape around the seat a few times for it to stay on there. I also cut a little notch in it so that it would fit snugly around the pole underneath the seat, but you can do what works for you.)
You can add on a seat belt, a bar, or whatever you want. We made a crude makeshift helmet out of leftover cardboard, as you can see on the bunny.
Let me know if you try this project! And don't forget to check out this giveaway (until Nov. 5) if you want a chance to win some Japanese stamps.