Can a man with down syndrome get an erection and have kids?

Males R not fertile: While the Down syndrome female is fertile, the male is not. A few exceptions may be seen if a mosaic male (being normal in some cells & ds in others) has a normal cell line in his testis. But mosaics represent <2% of ds males. Whether or not they might become aroused or not is probably specific to the situation. These kids or adults are often the victim of abuse in many forms.