Why do toy stores try to sell toys just before Christmas?

There are children whom Santa Claus doesn’t give presents, due to their misbehavior.

Daughter: (Looking at advertisements inserted in a newspaper) [Alternatives: "(Looking at newspaper advertisements)", "(Looking at advertising inserts in a newspaper)" The word "inserted" is only correct if these are extra pages which would not normally be in the newspaper. If you mean advertisements on the ordinary pages of the newspaper, "newspaper advertisements" is the most natural phrase.]

This is a secret, so don’t tell others. [Alternative: "... don't tell anyone (else)."]

There are children to whom Santa Claus doesn’t give presents, due to their misbehaviors. ["To whom" is grammatically correct here, but omitting "to" is extremely common in spoken English. The noun "behavior" can be used both as a count noun and as a non-count noun, but for the meaning you want, it is a non-count noun. "Behaviors" means specific types of actions; "behavior" is overall style or quality of actions. The non-count use is more common.]

Their parents feel sorry for them, so they secretly buy presents for them and make (their children) believe that Santa Claus has visited them. [Alternative: "... and pretend that Santa Claus has visited them." "Their children" can be omitted; "make believe" without an indirect object is a synonym for "pretend." If you want to include the indirect object, you can also say "... and pretend to their children that...", but "to their children" is not necessary.]

This is what my husband actually heard from one of his friends some years ago. [Alternative: "My husband actually heard this from one of his friends..."]

Daughter: (Looking at advertisements inserted in the newspaper)