For beginners there is no need to have a leotard or club tracksuit, these are only needed if they are entering into competitions.

Shorts or tight leggings with a long sleeved tight fitting top (loose T-Shirts fall down around the gymnasts head and can be dangerous). Gymnastics shoes, socks or bare feet. Socks are essential for the Trampoline.
Strictly no jewellery as it is too dangerous, if they have a small piercing that cannot be removed at the moment it can be taped up with a small plaster.