I'd say this is definitely a noticeable thing with small children at family gatherings, birthday parties and the like. But I grew up in a household where both of my parents came from families where big family gatherings with even extended family was common, and I know not everyone has that kind of experience, so who knows how much of that is nature or nurture as well.
In my case however this has persisted well into adulthood: despite being a chronic insomniac who has a really hard time falling a sleep normally, at these types of social gatherings I often have to fight off falling asleep precisely because I feel comfortable and safe among friends and/or family (I wonder if that is in any way related to my ADHD).
It's the food and air quality. There's a lot of people in an enclosed environment eating too many carbs (or too much in general).
Timing is critical and I'm on a mission. Before the heavy food comes out, I grab a seltzer and a small salad. I convince some people to join me on the patio for a drink. It's important to arrive late enough that people are eager to break away, but well before any food ceremony.
[0] https://youtu.be/5IPQIl-FiCY?si=drUMJuR5tLLppWqD&t=738 relevant section is 13:00 - 14:00 of a 30 minute video about various inn / tavern aspects.