First let me say that we need more specs as far as lower grade work is concerned. But is the highlighting of these words really necessary when they are also shown in bold in print? It just seems like a little over kill.
BANA is currently working on guidelines for early learning materials.
The transcriber can decide to not include any emphasis that doesn't add any meaning...so if you feel the text adequately explains things, you do not need to include it. Without seeing your print, I can't answer this definitively.