What it teaches
That brackets decide what happens first, and that this changes the result. (3 + 4) × 2 is 14 and 3 + 4 × 2 is 11. Nothing about the numbers changed.
This is the first rule in maths that is a convention rather than a fact about quantity — and children accept it much more readily after they have seen the two answers side by side than after being told the rule.
What to look for
This belongs to the last level of the maths games and to klasa IV in the Polish curriculum. A seven-year-old who wants to try it will not be harmed by it, but the arithmetic inside the brackets has to be secure first, or the child is fighting two problems at once.
The most common mistake is doing the sum left to right and ignoring the brackets entirely. If that is what is happening, the answer will be consistently wrong in the same direction, which is easy to spot.