Shin Guards
In your best interest to wear these, as well as compulsory for most games. They come in different materials so try on and find what feels the most comfortable; it should offer good protection but not stop movement.
A popular type are those that loop under the foot and then held in place on the calf with Velcro. They usually have extra padding around the ankle and Achilles tendon, which is particularly important for strikers.
Fibreglass gives great protection and is very lightweight making them a good choice for young players. Plastic are the cheapest and still give you good protection.