Well, you're not going to be paying medical insurance for eternity. Till each child turns 26 at most. Unless the child is disabled, and not always then, you CANNOT continue to carry them on the insurance past their 26th birthday.
Let's address this from another angle. Some employers have what's called two tier insurance, some three tier, and some four tier.
In two tier insurance, there is only individual coverage or family coverage. You pay one amount for just yourself, but when it comes to family coverage, it doesn't matter if you are covering one dependent or ten, you pay the same amount.
In three tier insurance, you pay one rate if you're covering just yourself, a different rate if you are covering only one dependent, and a third rate if you are paying for more than one dependent.
In four tier coverage, you pay one rate for just yourself; a different rate if you are covering yourself and your spouse, a still different rate if you are covering yourself and a child (or children) but not a spouse, and finally a fourth rate if you are covering a spouse and child (or children).
Which does your employer provide, and who are you currently covering?