addChild within addChild?

I have a addchild within addchild, simplified;

var mama = new effect_pj_8_rotate();
addChild(mama);
var baby = new letter_pj_8_rotate();
mama.addChild(baby);

Now the Library item letter_pj_8_rotate contains a text field with instance name lettervalue. If I add the following line

mama.baby.lettervalue.text = “w”;

It doesn`t set the text field to letter “w” but gives output
TypeError: Error #1010: A term is undefined and has no properties.
at PJ_8_rotate/::frame1()

Anybody see any syntax error?