At Alic in Puerto Plata you?ll find a mixture of children, both expats and Dominican children.
They do not need to know Spanish.
The first year I was here, I asked to skip the French lessons for my son, as Spanish was enough. When class had French he had private lessons in Spanish instead.
Kids do pick up the language fast, in playing, in meetings with people.
As for picking a place to live, come here first on a longer term, feel the places.
Ask yourself issues such as where do you and your family want to live, what is important to you.
Are you talking about adapting to a more expat society ( Sosua ) or the local society ( Puerto Plata, Santiago etc ).