Having children impacts your career (assuming you make choices with them in mind) because suddenly, long hours are less appealing, you can't put all your energy

Having children impacts your career (assuming you make choices with them in mind) because suddenly, long hours are less appealing, you can't put all your energy and time into your job, and a job you can hang onto for 5-10 years is more appealing (moving a lot with young children is a royal PIA). Regarding job safety when you can get another right away: Finding and getting another job is stressful. You have to acclimate to a new environment. You probably have to learn or relearn some skill. So while doing this once every 2-4 years is fine, every couple of months or even once a year is disruptive.