Making Unschooled Kids Learn Maths Just in Case

Should we make our unschooled kids learn maths in a formal way just in case? Is this sensible? We never know when they might need to prove they have covered all the skills presented in maths courses. What if they want to apply for a university degree course that has a maths prerequisite? What if our kids decide they'd like to go to school and so have to slot back into the system with their age peers?