Where in Mexico are you based?
Public education is free but is not of an equal standard to private tuition. Generally, schools in the more rural regions suffer from poor service delivery and high dropout rates.
Alternatively, schools in urban areas tend to perform slightly better. Grades 7 through 12 must pay for textbooks, with younger grades below that receiving them at no cost.
The most popular option amongst expats when searching education in Mexico is homeschooling combined with public school. Learning the language and growing up with local kids will definitely help their integration and understanding of society. It may also be easier on your expenses.
What grades are your children going to enter?
Hope this helps.