Math Foundations includes number sense and knowledge of operations.  Children need a basis of being able to recognize the number in a group without counting (subitize), counting, compare the size of collections, and using numerals to to quantify a collection.

An example of a developmental progression of number knowledge includes:

• Subitizing (small number recognition)

• Meaningful object counting

• Counting based comparisons of collections larger than three

• Number-after knowledge

• Mental comparisons of close or neighboring numbers

•  Number after equals one more

 https://ies.ed.gov/ncee/wwc/Docs/practiceguide/early_math_pg_111313.pdf

Having adequate number sense is a fundamental skill for acquiring and developing complex math concepts.

https://www.u-46.org/Page/11457