It would actually be a bit easier if you developed a coding system that put everything on a single line. You can read Chapter 6 of the CLAN manual about how to use Coder Mode to do this, and chapter 14 of the CHAT manual described the INCA coding system of Ninio and Wheeler that exemplifies the approach. In your case, for example there would be codes such as $err:* and $rea:* that characterize the errors and the responses. The asterisk indicates some further levels of the coding system you might create. You can then use KWAL search patterns to track combination of errors and reactions.
This can also be done, as you suggest by simply merging the two types of information into single codes, again within the general framework of systems such as INCA. Actually, I think that is the most straightforward approach.
You may feel that it is necessary to separate this information so that errors are coded for the child and reactions for the adult. In that case, you can create more complex search strings using cross-tier COMBO, as described in section 9.4.4 and 9.4.5 of the CLAN manual.
Best regards,
— Brian MacWhinney