Based on what you're saying, it seems that you need to include your child's information on your own Form 8938.
It sounds like you're filing Form 8814, Parent's Election to Report Child's Interest and Dividends and electing to include certain unearned income of your child on your own return.
In that event, you -- the parent -- are considered to have a financial interest in your child’s foreign financial assets, and therefore the accounts have to be accounted for on your own Form 8938.
Please see Interests in Assets Generating Certain Unearned Income of Children in the Instructions for Form 8938 for more information.