thirteen thousand seven hundred twenty
сёртин соусанд севен хандред твенти
My name is Svyatoslav. I will show you my family today. Here is my father, here is my mother, here is my brother Mark and it's me. I am 8 (eight) years old and my brother is 6(six). We are having a walk in the park and playing with a quadrocopter.
Children это множественное число.
Детей сосчитать можно, и есть форма единственного числа - child.
Так, что это исчисляемое.