I don't feel qualified to judge activities designed for kids, because I've
never taught physics to kids, so my remarks won't be comprehensive.
In Interaction #5 (two high energy photons collide and produce an electron
and a positron), I suggest deleting the sentence "The energy of the photons
can be calculated by multiplying their frequency by something called
Plank's Constant (E = hf)." The sentence introduces extraneous information.
No high-energy experimentalist would mention the frequency of a high-energy
photon; the photon energy is just stated as the photon energy; one doesn't
calculate the energy by evaluating hf. I see that this also comes up in
Interactions #4 and #7.
Also in this exercise there seems to me to be some possible terminological
confusion. Here is found the first mention of "moving energy" (presumably
kinetic energy), but there doesn't seem to be any prequel to this concept.
In the sentences referring to "particles," there is possible confusion as
to whether one means only the electron and positron, or whether the photons
are also "particles."
In many cases the text is careful to say that mc^2 is the rest energy, but
often we see the formula E = mc^2, which can be quite misleading. Probably
one should say E_rest = mc^2, or some such, since the energy of a particle
is gamma*mc^2.