Not the parent, but:
I use Anki constantly to study Math (or really any technical stuff, but Math is what I mostly study). I would never study without it again - I'm still unhappy that I did an entire 1st degree in CS before I knew about Anki, and barely remember most of it.
The more I use Anki to study Math, the more cards I tend to make. I usually make a few different kinds of cards (usually as I'm studying a textbook):
1. Definitions - usually something like "What is Normal operator? [Define]", with the back being something like "A Normal operator is an operator that commutes with its adjoint". I might add a bit more detail and flair (depending on the context).
Sometimes it's a more complex definition, e.g. "What is a group [Explanation, 3 axioms]", with the back being an overview plus the group axioms.
2. Basic theorems/properties - no proofs, just something like "What kind of matrices always have property X", "Orthogonal matrices".
These are often hard to phrase right, since it might be far too ambiguous to remember 2 years from now. I try to use these semi-sparingly.
An easier example: "What is the project of vector U on vector V", answer: "<u,v>/<v,v>v". (Again, I'm omitting details here like saying "in an inner product space", etc.)
3. Proofs - I tend to use these a lot these days. I'll often either just make a card for a proof "Prove that a compact set in a metric space is closed".
I'll also often err on the side of adding a proof, instead of using a "thereom result" card like in my point 2 above. E.g. instead of asking what is the project of u on v, I actually have a card saying "what is the projection of u on v? Answer and prove". That way I can always reprove it in my head. I usually do this when the proof or explanation is short, if not, I might just split it into two cards (one asking the answer, one asking for the proof).
4. Calculations - I have cards for base calculations if the subject warrants it. E.g. "what is the result of this matrix multiplication". Or even simpler things - I realized while studying math that I forgot a lot of even trivial stuff from high school, e.g. how to factor quadratics using "complete the square" - so I have cards with a few examples of this that I need to solve.
5. I also have some basic facts that I want to memorize, e.g. "derivative of ln(x)" or stuff like that.
Note that while I use Anki extensively for Math, I actually use it for lots of other stuff too.