We just came back from 4 nights at Hacienda Tres Rios with my fianc©'s two children and have very good things to say. The rate they quoted us for our wedding accommodation is $179 per person, per night, but that is all-inclusive. What I liked the best about it was that it was definitely family-friendly, but didn't feel overrun with kids/families; there was also an adults-only pool, so your guests without kids can also feel comfortable. (Bottom line: I would stay there even if we didnt have kids.) If you plan to do your wedding ceremony and reception all at the same place that you intend to use as accommodation, then Hacienda Tres Rios will be a great choice because they have lots of available venue options--from a river-side terrace, to gardens, to dining rooms, to beaches and private lagoons--that are really great! We are having our ceremony and reception off-resort, but several events will be on-resort (welcome cocktail, rehearsal dinner, post-wedding brunch) and I'm very happy with the venue choices, and the supplemental price per person for each of these fully-catered private events is really helping us control costs (a supplemental charge of $20 per person means that for our 60 guests, it will only cost us $1,200 per event.) Finally, each room can accommodate several people if your guests want to share rooms to control costs; there are two queen beds and a sofa bed in each standard room.
Otherwise, the Paradisus La Esmirelda is beautiful and has both adults and family sides, as does the Real resort chain. I would also recommend the Omni Puerto Aventuras as a very budget-friendly, family-friendly option! There is tons for guests to do in the little village there.