Ta'anis 30a - Learning on 9th of Av

The gemara cites the pasuk of "pikudei hashem yesharim" only as a reason for not learning with children, but not as a reason for the issur talmud torah. Although Rashi says that this is also the source for the issur Talmud Torah for adults, the maharsha says that for adults it is not necessary to cite the pasuk as a source. We find that there is an issur to be mesiach da'as from aveilus (see rashi 29b regarding washing clothes in the week of 9th av), so this would also be the reason to forbid learning - it is a hesech hada'as from the aveilus. This peshat is very difficult bec. we find that the Tana Kama allows to learn in areas that are not familiar. If the issur was simcha, then the tza'ar of trying to figure out something new would take away the simcha. Similarly, the tza'ar of learning iyov and other tragic stories would take away the simcha. But, according to maharsha who says that the issur is hesech hada'as, why should it be mutar to learn something new and something tragic?
We find that the Biur Halacha writes that concentrating on davening and learning while wearing tefillin is not considered a hesech hada'as. The reason is that the Torah doesn't demand concentration on tefillin, but rather any concentration on devarim shebikedusha is included in the kavana that is required. Similarly here, the issue of hesech hada'as only applies if one is mesiach da'as from the sadness by doing something which is mesameiach. Therefore, learning things that do not bring simcha i.e. new things or tragic things, is not a hesech hada'as. The point of the maharsha is simply that for adults this concept is clear without citing a pasuk - but when learning with kids one may of thought that it will not be enjoyable and not constitute a hesech hada'as. The pasuk teaches that the learning b'etzem is mesameiach and therefore even learning with kids is considered a hesech hada'as.