膝下

膝下	xī xià	at the knee (in reference to children) / (salutation used in letters to parents or grandparents)
膝	xī	old variant of 膝
膝	xī	knee
下	xià	down / downwards / below / lower / later / next (week etc) / second (of two parts) / to decline / to go down / to arrive at (a decision, conclusion etc) / measure word to show the frequency of an action