It is very difficult (in fact almost impossible) for a child diagnosis with Down Syndrome to purchase an insurance. I am glad to see one of my business partner, NTUC Income, offer the first insurance plan to cover this gap.
For more information on this product, please drop me a mail at kimheng@firstprincipal.com. Alternatively, you can read up the information at http://www.income.com.sg/insurance/SpecialCareDownSyndrome/index.asp and drop me a message if you need any clarification.