Some great advice and suggestions above, I visited a lot as I lived in Malaysia.
You can also use hand sanitiser to get rid of leeches, pour it over them, never pick them off! Buy socks etc in the UK they will be better quality.
You can also get Jungle Formula for children without to help keep off mozzies, and we only use 50% deet for ourselves again buy before you go along with sun protection , you can get sun lotion there (in Guardian, Watsons etc) but I always preferred to take it with me. Also a tip, buy some cream again in Watsons etc (like Boots) called Mopiko, in a green, red and white tube, its a Japanese cream for biting insects to help with the itching and helps take the sting out of bites, if you have a really bad bite put lots of cream on and cover with a plaster, its magic. We have had the delights of Dengue so cover ourselves thoroughly with spray when we go out and always long sleeves and trousers on an evening as we are an all you can eat buffet.
Being used to the heat etc I used to wear jeans (still do but in a different hot country) but lightweight cotton or linen is good, but outside the hotels I never wore shorts, make sure any shoes you take are worn in as well so no hot feet for blisters.
Rash vests are really good and I never go in the sea or a pool without one, great for kids and plenty in the sales at the moment. Also a hat with a spf is what I use, eyeing up a Tilly in the sale, but you may not need one. Dont bother with a special hairdryer, you will prob be a sweaty mess not long after you have done your hair, tie it up, slides etc if you can!
Both Craghoppers Nosilife and Jack Wolfskin anti mozzie clothing is good, but really only if your going hiking or trekking, again shop around and you can get some good prices.