What does the word mean?

What does "they" indicate in the below passage? "Nonsense and silliness"? or "kids"? or "adults"?

By any chance, if "they" means "adults", does the sentence seem right to you English native speakers in terms of context?

Probably the biggest roadblock to play for adults is the worry that they will look silly, improper, or dumb if they allow themselves to truly play. Or they think that it is irresponsible, immature, and childish to give themselves regularly over to play. Nonsense and silliness come naturally to kids, but they get pounded out by norms that look down on “frivolity.”