Biking with your kid in a seat attached to your bike is a great way to get to school! Front-mounted child seats are generally intended for younger kids since they have a lighter weight capacity (usually around 30 lbs) than rear-mounted seats. You can get seats that attach to the top of a bike rack or ones that attach directly to your frame. Some are removable and others are more permanently attached. Your local bike shop will probably be able to give you a good recommendation as to what will work best for you, your kid and your bike.
If you’re using a rear-mounted seat, remember not to wear a big backpack as it might squish the child. Make sure the seat provides a good way to secure their hands and feet so that no extremities can get caught in the rear wheel of the bike.
HOT TIP: A center-mounted double-legged kickstand will help the bike stand up on its own and can make it a lot easier to load and unload the child.
Another versatile option is to get a trailer that can attach to your bike. Many modern trailers also convert to strollers so that they can do double duty. These can also allow you to carry more than one kid with you (or a kid + one large dog, or one kid + groceries or any combination thereof). Just remember to attach a flag or balloon to the back of a trailer to make it more visible to other road users.
Two or three-wheeled cargo bikes (the ones with the big buckets in the front) are the minivans of the bike world and can be a great way to commute with your kids. They can even be equipped with winter tent-like kits that help you and your kid riding all year long! Though, cargo bikes can be a more expensive option (when compared to other bikes but not when compared to a minivan) and can be more cumbersome to store given their greater weight and size.
Trailer bikes and tow bars
If your kid is almost but not quite ready to ride on their own, you can get a trailer bike that attaches to the back of your bike, that way they can contribute to the forward momentum of riding but don’t have to worry about steering or braking. You can also find tow bars that attach an adult bike and a kid’s bike and have the same principle as the trailer bike.