My mate is ill so my other mate wants to take his 3 year old son tomorrow, will this be ok? Obviously if it was an adult trying to get in on a child ticket there would be a problem
No problem.
They have a light system on the turnstiles that shows up the class of ticket(Adults get a green light,my 6 y.o. Grandson gets a green and an orange) a steward monitors the lights to ensure you aint sneaking in on a kids ticket,but you will have no problem getting in a kid on an adults ticket.
Presumably should n't be a problem, but all the turnstiles have lights - when a ticket is swiped a child's ticket lights up just the green light an adults green & amber, I have seen stewards checking with a father & son who used each others by mistake.