I don't think it means that. It's just that it is impossible to work with those childlike feelings therapeutically when they are not coming into the session but are floating somewhere outside in the emails.

It might sound harsh, but you and the therapist are there together for one particular reason - to help you and the only things that he can really help you with are those things that you are able to bring into session. Thus, because he cannot help you with those things that you don't bring into session but rather express via email, there is no reason for him to engage with these things.

It is not that these things would not be valuable but in the context of this specific relationship they are useless because they cannot be worked with to help you. The therapist would be unethical if he would engage in activities that do not benefit you or that do not have therapeutic purpose.