Free range is really cute but indicates some level of choice for the children involved. When the kid has little or no choice in her "freedom" it's not really freedom at all.
But she did have choice. She's the one who asked to spend the day at the park, instead of hanging out all day at McDonald's, which is what she had been doing. The option was always there for her to go back there if she was tired of being at the park, as far as I can tell - apparently she did go there for lunch.