Question

The childern as well as their mother ____ ( is/are) missing

Answer 1

The children as well as their mother are missing.

Detailed answer

The most appropriate answer to this is the word "are" missing.

• This is the most grammatically appropriate word to be used at this moment.
• The word "are" is used to denote "present tense and second-person singular"
• If we had used the word "is" it would have created an incorrect subjected-verb agreement.