I don't think the mom should have been arrested, but letting a seven year old walk a half mike to the park, play alone, and walk back, in a neighborhood with pedophiles is pretty poor judgment.
Community notification of registered sex offenders began 1994. Surely there have always been pedophiles in every neighborhood. We just didn't know where they lived. Potentially, there are pedophiles is all neighborhoods, whether we know they live there or not. While I agree that it is errant to send a child out to play where there are know pedophiles, assuming this mother knew of this, is it not better to give your kids the tools to know how to deal with this treat should it ever occur? When the boy was questioned by someone at the pool, he did what parents have been teaching their kids to do for a long time and that is not to talk to strangers. He did this by fleeing the scene.
A half mile is ten city blocks. In Oregon, school bus transportation is not required unless the student lives more than a mile from school, which is 20 city blocks. This law does not address the risk of them being approached by pedophiles in the neighborhood. I could not locate the Florida school bus transportation laws, but let's assume they are not markedly different from Oregon's. This would mean a parent can allow their 7 year old to walk to school but not to a park which is potentially closer to home than the school.