The Stones have three …in the family.
a)childrens
b)childs
c)children​

Children

Объяснение:

Child-children(исключение)

ответ: c ( children ) (так-как "childrens" "childs" только единственное число)

Можно лучший?)

1. i exercise regularly in summer but more to do in winter. 2. she usually walks slowly but now she is walking even   faster . 3. nina speaks loudly but mary speaks even   louder . 4. he runs fast, than other boys. 5. i don’t sleep enough, less   than 8 hours. 6. he behaves badly, than other boys. 7. i smile often, more than my sister. 8. peter lives far from school, but ann lives closer .

я думаю, что  4 и в 6 предложениях ничего изменять не надо. может я ошибаюсь.