If your child has the academic ability to take Maths and Further Maths at A-level, they should deffo do so. I'm currently studying Biology, Chemistry and Economics and wished I had taken Maths and/or further maths instead of one of the sciences.
Many degrees require mathematical ability, and if your child has the academic ability to take Maths and Further Maths, I doubt that they'll go to any university that isn't top 20 (provided they put the effort in). Economics at degree level, for example, requires A-level Maths at most 'good' unis.
If your child would like to study an English-based subject at university I would recommend Maths, Further Maths and English Lit. Likewise with something like Physics or Chemistry, they should be taken as the third subject.
Economics is more maths-based than business-studies true, but even Oxbridge do not require you to have studies Economics at a-level for you to apply to their BSc in it.
Tl;Dr is that Maths and Further Maths typically have more clout than tany othersubjects at A-level -good mathematical ability is regarded very highly. As mentioned by another user in this thread, make sure your child is doing subjects that they enjoy. I'm not enjoying chemistry and it pains me to bring myself do to any chemistry revision or homework. Oh, and make sure you are not forcing your children to take any A-level they don't specifically want to, only encourage them to do what you believe is best.