Isabella, don't take the promotion now.  The most precious years are when the kids are tiny, and the bond formed then is the most important one in life.  

If you are being offered an executive promotion now, decline with thanks and explain your situation.  Be clear that you would be very interested in a few years once the children have developed a bit of self-sufficiency.  Family is far more  important than career.

Corporate Governess says you should avoid the nagging "What if?"  My counsel is that the selfsame question will be asked when you realize you spent the best years of your life in thrall to your employer rather than your loved ones.  No one wishes they spent more time at work on their deathbed.