I would be surprised if loitering laws are even enforceable today. I can see trespassing if you're asked to leave and don't, but getting arrested for being in one place too long? Especially a public place like a park? I'd donate to that gofundme. Kids could learn something from first amendment auditors and just start filming themselves in public.
Very few children know enough and have the disposition to productively stand up to a cop (or any other seemingly legitimate authority) and try to defend their rights. Legally, whether they have the same rights as adults is also questionable.
Parks have operating hours. Cities have noise ordinances, etc., to give Cops options for booking who they want for whatever they want. Cops don't necessarily care what the laws are, anyway. I've taken a ride in paddy wagons to a station before for hanging out in a playground because a neighbor said we were causing trouble. We were just talking. No, we weren't processed, but we were left to figure out our own way back home. This was in the 90s. The same stuff happens today though.
The small rural Canadian town I grew up in (~2000 people) during the 1990s had a real estate agent that would call the cops if he saw any teenagers out after 9pm. He would literally lie to them, saying we were causing trouble if we were just walking to the convenience store. He was trying to keep the town "desirable" or something. This man fought anything that would keep teenagers occupied. Skate parks, benches, etc. My group would lay in the park during the dog days of summer just chatting and passing around a jug of orange juice, which he would tell the cops was spiked with vodka (which we did do, but never in the park).
Of course, we (as in the teens in general) probably fed into his paranoia - let's just say harassing the neighbourhood teenagers rarely ends well...
Compare how things were back then to now and this RE agent probably stroked out from the mannerisms of the recent newcomers