Corner flags are easy to make and it is a simple volunteer task for parent on the team. It is traditional to match the flag color to that of the team uniform.
See the instructions below and feel free to improvise. The laws require that the flags rise to 5 feet or more above ground, the flag to be about 1 foot square and be made of brightly colored material. The tops of the poles must not be pointed. We recommend using 1/2" irrigation pipe (Schedule 40) for the poles. The flags can be glued to the poles with any convenient cement. It is also possible to purchase ready made flags from soccer suppliers, for example the AYSO Supply Center, 1-888-243-AYSO (2976).
Some fields may have corner flag holders in place - essentially a larger diameter piece of pipe embedded in the gound into which you can insert the flag pole. Otherwise, the pole must be pushed as firmly into the ground as possible. An angled cut on the base of the pole can make this task somewhat easier.