While bullfrogs can be fascinating to raise from the tadpole stage, and while raising them can provide countless educational opportunities to children, they nonetheless are not the best candidates for pets.
Bullfrogs should not be handled. The oils from our skin can be harmful to the frogs, and similarly, the frogs can be carriers of dangerous salmonella. Because bullfrogs can live so long, you should be sure that you'll be able to commit to caring for your frog(s) in the long-term. If your child's interests are varied and quick-changing, you might want to reconsider your choice! If you can no longer care for your bullfrog, you must be very careful about releasing your bullfrog into the wild unless your bullfrog was native to your area. Non-native bullfrogs are considered invasive species, and can cause quite a lot of damage and disruption to local ecosystems. Because bullfrogs are known to cannibalize, it's recommended that you keep only one mature bullfrog in a tank.