I have an iBert Safe-T-Seat front bike seat for sale. It attaches to the front of your bike, creating a better centre of gravity than child bike seats that attach on the back. It can also be more fun for your child because it allows them to see where you're going.
The seat is recommended for kids from about 1 year (they have to be able to sit up straight and wear a helmet) up to about 38lbs, although it will depend on the height of you and your child so that you can comfortably see over their head.
The seat is in like-new condition. Instructions and more pictures can be found online on the iBert website. Let me know if you have any questions!