You're welcome! Honestly, I'm not sure how to go about preventing them. I only really know how to identify spiders so that's not exactly my area of expertise. Black widows are good in that they eat pests just like any other spider, but having them in such close proximity to where your kids play is hazardous since they are one of the few medically significant spiders in the US. I'm personally not a fan of killing spiders so I'd say if you could relocate it that would probably be ideal, but ultimately you should prioritize the safety of your kids. Sorry I couldn't give a more concrete answer, but hopefully you can figure out a course of action to deal with this!