My boy?

Currently, Kai is totally fascinated by numbers. Several times a day, looking totally serious, he goes
"muuuuum ... eight plus three equals eleven"
"eh... yes"
"and nine minus four equals five"
"eh... yes"
And like that, he goes on. Today he made me do this, and was so thrilled he didn't even have time to go out with Keisuke. He will get over it, I guess?