Originally Posted by Play Care:
This.
I would only do it if I was getting a LOT of support/services from outside. I worked in a Day Hab for young adults with developmental/intellectual disabilities. A couple of the folks had DS, and were at times fairly aggressive (more so than the others) often "cranky" etc. We had to be extremely cautious around young children because they could be far too rough with them - and yes, sometimes intentionally. I know these were young adults not infants/toddlers, but both came from loving, supportive homes.
As others have pointed out those with DS often have heart problems as well as issues with eating, etc.
I don't say this to be a Negative Nancy. As pointed out about I think there's a perception of those with DS out there that's not entirely accurate. 
I don't take DS children because of this. They are often "moody". Like say they like playing with a toy or child one day and the next day the exact thing that made them happy will make them RAGE. Hitting, screaming, bitting. I often feel like the other children and I have to walk on egg shells. I've worked in the board of ed before with therapists and other spec ed professionals. They would tell me nothing happened. They were just frustrated and nothing would have predicated it. I know this sounds unkind, but they will often terrorize the other child. I don't think group settings work. Even in schools they often need a one to one.