I have a canon rebel T6 what lense, external flash should i get to take pictures of kids?

I’m new to having a camera and I’m not sure how everything works with my dslr. i have a T6, and i would like to take pictures with flash without the kids squinting and that it is fast when I shoot. Also do you know of any websites to learn about aperture mm, and all of those details? I am not sure how i should be choosing the lenses. Thank you!

Taking Photograph Through Beamsplitting Glass so the object photographed cannot see camera lense back

I am new to beam splitting glass & its properties and possibilities, but I would like to think that it should be possible for me to some sort of beam splitting glass in order to be able to take a relatively clear photo of an object on the other side of the glass.

And, from the other side, from the objects view, if you were to look at it – possibly shining a light at where the camera lens should be, the light is refracted off the beam splitting glass and thereby not reflecting back.

If anyone could please help me with this problem or even point me in the right direction it would be greatly appreciated. It is hard to get in contact with a lot of the beam splitting glass manufacturers – big and small