Congratulations on your new grandson! My husband and I have a 7 year old son with d.s. and he (and his little brother) are the loves of our lives!
I would be very surprised that the o.b. who delivered your grandson( or the pediatrician) wouldn't have mentioned the possibility of d.s. to your daughter when he was born. (There are a lot of babies who sometimes "look" like they may have d.s., but their features change as they grow)
The most definitive way to find out is through a blood test. However, some of the other features are: almond shaped eyes that are slanted, flattened nose, webbed neck, deep crease inside the palm of the hands, low muscle tone, problems eating or sucking (due to low tone in the face) smaller mouth (tongue can often protrude).
Also, a high percentage of babies with d.s. can have heart problems which need to be addressed immediately.
There are also excellent early intervention programs through your community who are available to help with physical, speech and occupational therapy.
There are often local chapters for d.s. as well as the National Down Syndrome Society, a wonderful source for support. ([url]www.ndss.org[/url])
For new parents, having a child with d.s. can be a difficult thing to accept. But with time they will feel an incredible sense of happiness, joy and love.
Hope this is helpful. Good luck!