Parents: would you find this okay?

I would ask the mom ahead of time (not Saturday, more in advance than that) if it's okay if you bring the child with you to kickboxing practice. Depending on the age of the child, the mom might be fine with that. There's a big difference between watching you kickbox for an hour and going to the park. The park is fun for little kids, sitting still is not. I'd say if she's a little older 7+ then she might enjoy watching you kickbox. Any younger than that and she'll get bored and might wander off while you're not looking.