Tax Year Prior to 2020: should file tax for minor if loss a lot in stock

[stantonporsche]

My son's custodial account lost about $4000

My son did not earn any money in 2018

Can or should I file a tax return in order to take advantage of $4000 carryover loss?

[NCperson]

Yes

[KarenL]

If anything was sold in the account and he received a Form 1099-B, then yes he should file.   If the losses are in a Qualified (example an IRA) type of an account, or nothing was sold, then there are no carryover losses to be reported.