Answer:Los niños son alto.
Explanation: The subject and verb are in plural but the adjective isn't and it should be.
The subjunctive is a grammatical mood that expresses suggestions, wishes, etc. It also expresses doubts. When a sentence does not express doubt. The grammatical mood is not subjunctive.
E.g.
•Dudo que tengas dinero para mi almuerzo.
This sentence expresses doubt.
Whereas..
•No dudo que te mantienes en buena forma física.
The sentence does not express doubt.
