My daughter tried it last year (at 7 yr old). I think if your child does not scare of water, & could move forward by himself in the water, it should be ok. Or you could ask other participant to help and take care. However, you could not use any 水袖 or even goggle. I think it is worth to try.
Maybe my memory is wrong, seems last year I paid by credit card when I book it through Internet. At that time, they also said if my child scare and not willing go into the pool, could refund half of the amount.