The Prophet (sallalahu 'alayhi wa sallam) said, "Solomon (the son of) David said, 'Tonight I will sleep with seventy ladies each of whom will conceive a child who will be a knight fighting for "Allah's Cause.' His companion said, 'If Allah will.' But Solomon did not say so; therefore none of those women got pregnant except one who gave birth to a half child." ...WHAT'S A HALF CHILD?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.

The Hadeeth you have mentioned, dear Brother, is an authentic Hadeeth that was reported in both Al-Bukhari and Muslim  as is the highest level of authenticity. It was narrated on the authority of Abu Hurayrah . As for the meaning of "a half child," it means a premature or disfigured child. Some versions of the Hadeeth read, "except one who delivered a half person."

Allaah Knows best.