"LEss children" es muy usado, pero es incorrecto
Lo correcto es "Fewer children" debido a que es un sustantivo contable y plural.
He oido mucho decir less people
pero, obviamente no es apropiado.
Puedes decir "less time / money"
Although it may be considered incorrect by some, it still sounds natural to my ears since it's a very common "mistake". You should avoid it, though. It would be better to go with fewer, which is preferred here.
But, I still have some problems with less, I know I must use it for uncountable nouns, but for example, is ok if i say: I think, Governments should find less stressful methods to control the number of children that people can have.
I am trying to write an essay , so I will appreciate your help.