Why must it be armbands and not buoyancy garments?
Armbands and buoyancy garments have been tested by British and European Standards agencies to assess what is safe and what is not.
We recommend you use a form of buoyancy aid that has been validated in this way and make sure that any aid you use for your children complies with EN BS 13138.
This can be either a buoyancy garment or an armband. However, experience seems to indicate that armbands are usually cheaper and more readily available than buoyancy garments.