In reply to minimike:
I don't get it. Why aren't you climbing? I find my son learns as much from watching me and others climb as he does from climbing routes himself. if you think you don't have time to walk between the adult and child wall you are wrong. Bouldering needs to be taken slowly. The time spent on the ground can be spent giving valuable coaching, for instance, asking you 6yo what his plans are for climbing the next route.
The simple answer to the shoe hire problem is to acquire a pair for your 6yo. Children are growing all the time so the supply of good quality used shoes is great or otherwise drop into decathlon for a pair of these https://www.decathlon.co.uk/rock-junior-childrens-climbing-shoes-id_8240895....
That said, I have also noticed that many parents confuse climbing gyms as soft play. Releasing their children onto the wall and retreating to the café for a gossip. If charging entry to non climbers stops that sort of behaviour then I am all for it. Bouldering walls are dangerous places for unsupervised children and all those who have to endure them.
If you can't climb due to some infirmity or other physical limitation then I'm sure you can negotiate reduced or free entry at the wall.