Whatever the meaning, the children' is wrong; it requires a terminal 's' to make the possessive since the noun is, already, plural.
the spider belongs to the boys Oops, that’s wrong Correct solutions: The spider of the boys The boys' spider
how's that any different?? it's getting really difficult trying to keep up with what the program wants; a literal or a more meaningul answer
To add "belongs" is to add a verb. (Pertencer)
The spider belongs to the boys = A aranha pertence aos meninos