Question

the child's foot & tooth is aching convt to plural

Answer 1

the children's feet and teeth r aching

or

the child's feet and teeth r aching

Answer 2

The word plural means denoting more than one.

The plural form of the given sentence is The child’s feet, and teeth are aching.

The word ‘tooth’ is the singular form whereas the word ‘teeth’ is the plural form. Similarly, the word 'Foot' is the singular form whereas the word 'feet' is the plural form.