After learning to read would you move on to teaching maths or a second language? My son is 11 mths old and not sure which one to purchase and concentrate on next.
You could definitely do both if you wanted.
But if it’s a which to purchase next question, here’s what my line of thinking would be:
Dot cards are pretty easy and inexpensive to make. They’ve also been notorious for maybe not being as successful as you think it will be. (I still do them, via Little Math with my daughter. It can’t hurt.). The sensitive window in time for subitizing is under 2 (I believe).
Foreign Language, if you or close relative/friend speak one, could be free (freeing you up to make a math purchase). You can check for free resources at your library. Little Pim videos, etc. If you have Little Reader, you can get foreign language downloads and/or make some. The sensitive period for learning languages is under 7 (though I believe the earlier the easier).
I started Little Math and Little Reader at the same time when my son was about 6 months old and then a couple months later introduced him to Spanish and Chinese.