I can’t stand crowds so I wouldn’t recommend very many on a busy weekend. Trash & noise are not for me.
North coast- Caleton. But it’s very small and I wouldn’t go later afternoon on a weekend. Or go early to get a good spot. Bring change to pay for the bathroom. 10 pesos per visit. There were about 30 buses parked on the road alone this past Sunday at 2pm when I passed by, so I can’t imagine Semana Santa.
Any around Sosua and Cabarete have big waves. Depending on the day and size of the child, the waves can just be too much. I’m curious about Playa Magante- never been. Playa Grande is huge, but the waves can be huge as well.
All beaches I’ve visited in Las Terrenas are ideal, except the one at El Valle- it has bigger waves. Playa Las Ballenas, Playa Bonita, parts of Playa Popy are all calm, mostly shallower, and ideal for smaller kids.
Las Galeras beaches are calmer as well.
South Coast- Playa Juan Dolio proper is okay, but for a calmer area, see if Cafe Del Sol is still open. The beach there has very shallow water with a gradual decline and nearly no waves so it’s very safe even for toddlers to splash. It doesn’t get deep fast either.
Boca Chica is nice and shallow too for smaller kids but I prefer to have a free spot in the sand and shade as opposed to a $200 pesos plastic table under an umbrella next to screaming, vaping people, discarded styrofoam, and diapers.