Hon Lao sits in the Nha Phu lagoon, about half an hour by road from central Nha Trang plus a short boat crossing. It is universally called Monkey Island for the several hundred semi-wild macaques living there, descended from an earlier breeding station.
The monkeys are thoroughly used to people and will approach to beg. They are fast and bold — keep bags, glasses and phones secured, and never tease them or feed them by hand.
This deserves saying plainly: wild monkeys scratch and bite, and any wound from a wild animal needs proper medical attention rather than a rinse and a plaster. With children along, keep them within arm’s reach and don’t let them hold food.
Beyond the monkey area there is a beach, plus shows and beach games. Allow half a day including the travel.
Families tend to like it; if what you want is a quiet island to swim off, Hon Mun or Hon Tam out in Nha Trang Bay will serve you better — the water in Nha Phu is brackish and considerably cloudier than the bay.