Here are some items you can purchase from Amazon. These are meant for beginner not recommended for competitive gymnasts. You can participate lessons with items similar with these items.
Rope(better not to have handles on the edge. Slightly heavier rope works better for beginner)
Ribbon (Its better purchase longer than 4m)
Any hula hoop is good.
Ball (16cm-17cm is good for children. 18cm is good for 10 yo and older. Rhythmic ball works different from other fitness ball. So we recommend to purchase Rhythmic gymnastics ball. )