The plural of CHILD is CHILDREN
The plural of PERSON is PEOPLE
It is very common for a Spanish speaker to say “childrens” just following the general rule of adding -s to make the plural. But this is completely incorrect.
Thus: I can see a child eating and three children drinking.
It is very common for a Spanish speaker to say “persons” but this is partly incorrect. According to some grammars it is only correct when used in legal or formal contexts, and although you can hear it by some native speakers, it is preferable to use the plural “people”.
Thus: I can see a person running and two people smiling at him.