The only place you will be able to take your children swimming safely would be all the way in town where it’s very Leeward and protected. That’s where I take my young son swimming. It’s a beautiful area. Lots of culture. Cabaret is an amazing place. I’ve been going there for over 20 years. Truly the nicest people. The town is awesome. Amazing restaurants everything is fairly inexpensive. I suggest staying in the vicinity of the millennium east west in that area should be perfect. feel free to private message me if you have any more questions.
I go to Cabarete a lot but have yet to take my kids which are similar age. Best beach for them in my opinion is Kite Beach as the water is clear and no significant waves. It’s also right near the town so lots to do. Cabarete Bay (the windward bay) has murkier water on the shore and bigger shorebreak.
Millenium would be good to stay or some nice airbnb on kitebeach. The only negative is there really are a lot of kites and you wouldn’t want your kid getting hit with a line.
Encuentro is quite removed from the scene and is the surf beach. The waves are too big for little kids typically and it’s a reef bottom with urchins near the shore so it’s not good for the kids to frolick. You could stay at Natura Cabana which is a little farther leeward and super cool with good food and a nice beach, check it out.
Punta Cana is totally different and has terrible wind.