If you are booking online you'll be able to check any age restrictions on events. Just search the event you're interested in and select the correct date. Once selected you'll see "Event Info & Restrictions" on the top left, and at the top, under the event name, it'll say "Please Note" and the age restrictions will be there.
If an event does have an age restriction you will need to abide by this. Even if an adult is attending, some events won't let anyone under 18 attend.
Please note that for events that do allow children they must make sure they have an adult aged 18 years or over with them at all times.