Acquisition of 'how' and 'why' search

[Anne Graffam Walker]

Greetings.

Can anyone point me in the direction of research on the acquisition/use
of "how" and "why" by 3-, 4-, and 5-yr-olds?  As a forensic linguist,
I'm doing a study of those words which are critical in the questioning
of young children for forensic purposes.  Your help will be very much
appreciated. [One possible barrier:  I read only English.]

Thank you.

Anne Graffam Walker, Ph. D.
Forensic Linguist
6404 Cavalier Corridor
Falls Church, VA 22044-1207
(703) 354-1796
agwalker at erols.com