Is my retirement age realistic?

I'm trying to figure out if my FIRE plan is realistic, and I'd love your feedback. Here's my current situation:

Age: 31 Family: Wife and two kids Desired Retirement Age: 45 Current NW: 455k Income: 240k+ Annual Expenses: $80,000 (comfortable living) Using the 4% rule, my FIRE number comes out to $2M but we would like to have $2.4M

My questions are: Does $2 million seem like a reasonable FIRE number for a family of four, considering I want to retire at 45? Also, for those who have FIREd with a family, what advice do you have?