Numbers 0–20 for kids
The very first thing every mathematician learns.
Before addition, before subtraction — kids need to feel the shape of each number. Yaze uses subitising (recognizing a group instantly, without counting), one-more/one-less, and odd vs even to build strong number sense.
Counting to ten is not reciting ten words — it is matching one number word to one object and knowing that the last word said tells you how many there are. Most children say the sequence long before they understand it, usually somewhere between three and five.
Odd and even is a statement about pairing: line the objects up in twos and see whether one is left over. Taught this way (around ages five to seven) it stays true for any quantity, instead of becoming a rule about the last digit that children cannot explain.