Instead of guesswork, why not use one of those online calculators. Here's one:
USAA should have a similar calculator.
They all begin with your salary. They all should show how much monthly income your survivors will get from Social Security. That's right, surviving spouse and surviving children (up into college years) get money from the government. It can be a substantial sum. My spouse had college paid for by survivors benefits.
There is no need to pay off the mortgage "all at once." You just need enough insurance such that when invested it can provide for your income (less any SS payments), so that expenses including mortgage payments can be made.
For ourselves, we have no life insurance beyond what our employers provide because we are self-insured nowadays.
Just as important are wills with primary and alternate guardians for the children.
Don't forget: Receiving a life insurance payout is not meant to be like winning the lottery.