Then in my opinion you are using a tack hammer where a ball-peen is required.
Tag files are primarily intnded to replace tags whose primary output is pure JSP/HTML -- removing the need to build up HTML in
Java code. For the type of processing you are intending you would be better off implementing the tag as a Java class extending either the new "simple" or the "classic" tag support library.
If you do insist on using tag files, I would have the parent tag place information on the page context that the child tags could access and check with JSTL tags.