I know a few books in Spanish here in Argentina, but I don't think they are translated or shipped abroad. I participated in the Math Olympiads here, so my recommendation may be biased. I have a 9 y.o. daughter, so I hope it helps.
(I'm assuming your kid speaks English. All my links have official translations to other languages, that may be easy or hard to find.)
* There is an word wide math Olympiad for kids, we participate here. After looking for a while, they have some free material in https://mathkangaroo.org/mks/practice/free-question-samples/ (There are other sites in other countries/languages. I'm not sure if there is a better link.)
* Duolingo has a math course
* There are some nice videos in https://www.youtube.com/@Numberblocks (The firsts ones are very simple (aimed to younger kids), but the last ones explore more deep topics like factorization, squares numbers).
* Another set of nice videos in https://www.youtube.com/@SmileandLearnEnglish (My wife found it, they have videos of different topics, like math, biology, language, ... They have a many videos about math including basic operations and also long multiplication and divisibility rules.)
* My daughter is participating in https://www.matific.com/ at school. They have some online activities, she likes it but I don't see a free tier.