You can try this. It looks like the results you're after but why you'd want such bizarre results eludes me (enlightnment requested :-)).

SELECT PntKey=ISNULL(PntKey, Cd2PntKey)

,PntQty=CASE WHEN n1 = 1 THEN PntQty END

,FromDate1, ToDate1

,FromDate2=Cd2FromDate, ToDate2=Cd2ToDate

FROM (

SELECT p.PntKey

,p.PntQty

,FromDate1=Cd1FromDate

,ToDate1=Cd1ToDate

,n1=ROW_NUMBER() OVER (PARTITION BY PntKey ORDER BY Cd1Key)

FROM #Parent p

RIGHT JOIN #Child1 c1 ON p.PntKey = c1.Cd1PntKey) a

FULL JOIN (

SELECT Cd2Key, Cd2PntKey, Cd2FromDate, Cd2ToDate

,n2=ROW_NUMBER() OVER (PARTITION BY Cd2PntKey ORDER BY Cd2Key)

FROM #Child2) c2

ON a.PntKey = c2.Cd2PntKey AND a.n1 = c2.n2

ORDER BY PntKey