Try the following & stop when your child finds the activity too challenging as they do get progressively harder:
Sit down and see how far out to the side you can lean before losing balance.
Sit down and see how far forwards and backwards you can lean before losing balance.
Sit down and lean from side to side and pat the floor in time to the Hold on Tight song.
Hold on to something, e.g. wall bars, and pull yourself up and lower yourself down. Do it first with 2 hands and then 1 and also try it in time with the Hold on Tight song.
Sit facing a partner, and hold hands with your arms very straight. Next try with one standing up, keeping arms straight and then swap places, so as one stands the other sits.
Stand while holding on to something with 2 hands, e.g. wall bars, try leaning out, hold your balance and then move back in again. Start with one foot forward and 1 back and then try with feet together. You could also try with 1 hand and maybe even eyes closed!