Kuta's nightlife is intense, going from bar to bar and club to club until the wee hours of the morning. The streets are well lit and very lively until at least 3am. If you are not a fan of nightlife, there are plenty of discos in Kuta where you can have a lot of fun. One of the most popular local venues is the Hard Rock Cafe nightclub.
The best thing for kids to do in Kuta is to visit the Waterboom amusement park with its water slides, rides, and underwater tunnels. The most popular adult activities in Kuta are the special parks for bungee jumpers (Adrenalin Park, Bali Bangy).
If you want more relaxed entertainment, you can visit one of the local spas in Kuta. They're the cheapest in Bali, with two hours of wellness treatments costing just IDR120,000, and you'll get a big discount if you pop in during happy hours.
Be wary of women offering massages on the beach. When they approach you, be sure to keep an eye on your belongings and be very specific about the price and time of the treatment.