It's your wedding. Do whatever you want. With that being said, my sister is adamant on bringing her child to my wedding as well. I'm still having it on an adults-only resort. If you want an adults-only resort, pick one that is connected to a resort that allows children.
I've booked mine at Platinum Yucatan Princess on their rooftop. Doesn't cost extra to be on the roof and they allow children to be there since it's private. Unfortunately, if you are to do a semi-private dinner, you aren't allowed to have children there. You can have a private dinner where you can on the rooftop which costs extra. This place is located 5 minutes away from Playa Del Carmen.
La Perla Paradisus is connected to the family side, La Esmeralda. You can have the wedding on the Gabi Bridge. This resort has this asian zen feel and pump out a lavender scent throughout. I checked out this place when I was looking into diferent resorts to get married in. This place is located in Playa Del Carmen.
Hideaway at Royalton Riviera Resort is an adults only resort in a family resort. I think it costs $1500usd to book the rooftop. It's beautiful. This resort is in the middle of nowhere.lol. Close to Cancun airport.
Good luck searching! I'm pretty sure that the majority of the resorts have a non-beach option.