My two "favorites" involving children were, first, the Shangri-la Wuhan where I entered the lounge for breakfast just in time to witness two siblings having a food fight utilizing the food right off the buffet. Parents were oblivious and the staff were feckless.
Second favorite was the Grand Hyatt Taipei during the evening service where the kids (at least 10 of them) became so unruly that I asked the lounge manager if there wasn't a quiet place I could go to enjoy my drink and snacks. She told me to try the coffee shop or the bar downstairs. Confused, I asked but wouldn't that require me to pay? She smiled and said "yes". That was the last time I ever set foot in their lounge (and the hotel itself).