If price is not a concern (and you are comfortable taking your kids to a classy hotel), I would definitely go for the JW.

Both are beautiful and you can easily go between them. JW pool is nicer (infinity), but some guests may give you the "oh no, don't bring those kids over here" look. Ignore them.

The pool at the CasaMagna was just your basic rectangular pool, but has a nice huge jacuzzi. I imagine your kids will probably spend most of their time in the Caribbean water, which was beautiful. Although the surf looks rough, in my experience, it wasn't. Of course, always check for yourself.

Both hotels are amazing, and the employees were some of the kindest we've encountered at any Marriott.

We didn't do the Kids Club but we did take advantage of their on-site scuba lessons.

If you do stay at the JW, look into the Club 91 rooms. They offer many amenities that might work very well for your family.

Have a great time. And yes, the hurricane seems headed right there now