Hans Megie, 33, was charged last night with sexually assaulting his three foster children and trying to kill two of them.  He raped a 10 year old girl twice, and sodomized her 8 year old brother and 6 year old sister last spring.  He allegedly taped the two younger children's mouths shut, put plastic bags over their heads and chained them in a closet in an attempt to kill them, according to police.  The children were returned to their biological mother in September and told her of the attacks, which were then reported to police.  The Queens Special Victims Squad arrested Megie and charged him with two counts of rape, two counts of attempted murder, three counts of sodomy, two counts of unlawful imprisonment and three counts of endangering the welfare of a child.