With this structure, there is (in general) some potential for ambiguity with "as well as":
Five people talked to Alice, as well as Bob.
Did five people talk to Bob, or did Bob talk to Alice?
In your sentence there is little possibility of ambiguity, since it is unclear how "men and women" could fall to "many children", so either of your suggestions is fine.
By the way, the possibility of ambiguity can be eliminated by moving the extraposed phrase next to its parent:
When the earthquake began, at least fifteen men and women (as well as many children playing in the park that day) fell to the ground.