With all due to respect to the OP who may or may not have a well-behaved 7-year old, this is very much a policy of catering to business travellers rather than those seeking an "all-inclusive" resort.

I have been in lounges, especially at the weekend in parts of Asia, where locals have clearly booked a hotel room with the intention of treating lounge attendants as babysitters whilst they enjoy a meal / drink.

Which isn't to say that children are the only problem. I also appreciate when a dress code is enforced, rather than guests visiting the lounge in pyjamas or swimwear.