There are no beach resorts in KL as it's the city. If you are looking for beach try Lankawi in Malaysia - about an hour flight from Singapore or the usual suspects in Thailand - Phuket, Hua Hin, Koh Samui, Krabi. There's also the Shangri-La in Cebu and in Penang which are supp to be extremely child-friendly. Sentosa Island in Singapore also has a Shangri La, The Sentosa Resort and Spa and then the brand new resorts that just opened in Resorts World - Hard Rock Hotel.