J., I'm a mom of two but I also work for the City of Denton, so I had to respond. I checked into the things we offer and came up empty-handed for grandmother-based groups but I think it's a great idea. Meetup.com is a great tool I use it as well.
The City does offer various free programs through the Libraries and Parks & Rec, as well as low-cost classes that might be beneficial, too. Check out www.dentonlibrary.com for more information. The new PLAY guide is also available, which includes class information at www.dentonparks.com.
Good luck!
K. Roberson
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