Mui Ne is not a very big place, but there is a mini-golf...  That's a great way to spend some nice family time.
The Tropical Minigolf is a good choice:

• The setting is very nice.
• Each hole is quite fun.
• The environment is very peaceful.

Check out their website.
After a 18 holes mini-golf, why not staying there for a drink and enjoy a diner in the Tropical restaurant and bar
Address: 97 Nguyen Dinh Chieu