Hi there and welcome
A Youtube account is a Gmail account, they stopped seperating these many years ago. Creating a new Gmail account will not help here.
As this is a LGL39C it cannot be unlocked with the Gmail account, not all phones use this as a backup, including this model.
I wont take up anymore of your time here but you will need to reset the phone.
The whole point of the lock is to stop access to the data, and whilst its not something you wish to do, you are going to have to reset the phone. If it was so easy to bypass it, it would of been patched (The Galaxy S2 had a bug where you could bypass the lock and was quickly patched).
To reset you do the following
Turn the power off. Press and hold the Power/Lock Key + Volume Down Key .
When the Factory Hard Reset welcome screen appears, release all of the keys.
Press the Power/Lock Key to continue or any other key to cancel.
Press the Power/Lock Key once more to confirm or any other key to cancel.
Your phone will perform a factory reset
I am sorry this is the case, but I do not want you wasting anymore time on this when your only option here if you cannot guess the lock, is to reset it.
Anything though stored on the SD card will be kept, so if your son stored anything there you will have it back again after the reset, its just the phones internal memory that is reset.
If you have continued problems, or would like any additional information or assistance, please do not hesitate to let me know.
And if you can take a second to rate my service by clicking one of the stars at the top of the screen then submit, that would be greatly appreciated.