We're a big group (seven adults, two kids aged 3 and 6), can you recommend some beach areas that might suit?

I'll suggest one destination in the Gulf of Thailand and another on the Andaman coast. Which one you choose partially depends on when you're travelling. The rainy season in the Gulf starts around Aug-Sep and lasts straight through December. Rainy season on the Andaman coast is from around May-June through October, although in recent years it seems to be starting later and lasting into Nov or even Dec.

In the Gulf, Koh Samui might work for your group because it has plenty of private house / villa rentals. These cater for many budgets, from extreme luxury on the beach to rather modest options set down inland lanes. So if you're looking for a place to all stay together in one big house, with its own kitchen and perhaps its own swimming pool, consider Samui.

The areas that are quietest and generally considered best for families are Samui's northern beaches like Bophut, Mae Nam and Bang Po, as well as southern and western beaches like Taling Ngam and Lipa Noi. Chaweng and Lamai are the two busiest beaches and both have some seedy nightlife along with techno-blasting beach parties, etc., but there are rental houses along the quieter nearby inland lanes.

On Samui you have a solid list of attractions on the island, and those who want more adventure will find some of Thailand's most dazzling islands if day tripping into the nearby Ang Thong National Park. You could hire a private boat for that or book into a group tour. Another nearby island that you might find worth a day trip is Koh Matsum, where kids often enjoy seeing the domesticated boars that live on the beach.

Meanwhile on the Andaman coast, the Khao Lak area is not far from Phuket but much quieter and without the traffic jams and seedy nightlife (to be fair, several parts of Phuket, such as Bang Tao and Kamala beaches, are also good for families). Khao Lak might work for you because there's loads to do, including day tours to nearby Similan or Surin islands, both of which are also part of national parks and also rank among the most dazzling islands in Thailand. Or you could go to the sea turtle conservation centre or, if you're really lucky, even possibly see turtles hatching on nearby Khao Lampi and Thai Mueang beaches. Other kid friendly activities here are visiting the old town market in nearby Takua Pa, a boat tour of the magnificent Phang Nga Bay, miniature golf, the butterfly farm, and the night markets and many different beaches within the Khao Lak area.

Perhaps not ideal for younger kids but worthwhile for everyone else, is a visit to the deeply moving 2004 tsunami memorial just north of Khao Lak in Ban Nam Khem.