If you were in the USA, (not sure if this may also be a valid suggestion in your country) / go to a local bookstore - there are books/flashcards/activity books that are specifically targeted to common curriculum. Additionally look at your local school board to see if they publish (this is for elementary age school children) resources such as what are their 'word wall' words - like 200 common words children are expected to use/spell by grade 2. (some, they, their, our, the, them, et cetera).
There are common curriculum books that let you level set for a grade - which is important. Math may be easier, STEM subjects are hot right now. Language /reading is difficult for good content that has a consistent reading level. A lot of kids books will have a 'level 18' or 'Level G' - you can look it up, but in North America, a level 20 is what kids are supposed to be able to read at the end of grade 1. (short sentences, 8 pages, basic vocabulary).
tldr; pickup a kids school activity book and make a game similar to their examples. Don't copy, of course.