Alison: First of all, make sure to follow your doctor's advice, who will probably recommend to you products that contain Deet. On top of one of these products or in my case, as I'm actually allergic to Deet (a little unfortunate!), I suggest applying tea tree oil.
ABC have a great range of products containing tea tree oil. Firstly, there's pure tea tree oil. Simply add a few drops to your skin – particularly your hairline, ankles and scalp (that's where I seem to always get bitten) – or mix it in with your suncream (this shouldn't cause pigmentation problems).
Or ABC also offer tea tree oil in a bodycare skin wash formula which may be easier for the kids – just wash them in it every day.
Have a mosquito bite-free holiday!