You may find this post useful.
Although I don't have experience yet with PhD, I'll throw in the experience I do have as it might help.
This will be (hopefully I'll get in) my third time in the university with kids. I was pregnant at the age of 17 when I finished high school and started pursuing my BSc in Business Administration. When I started my MSc in Organizational Psychology my middle one was two years old. A better age but he was still breastfed and only started sleeping through the night at the age of 3, so it took a toll on me. Now my youngest will be one year old when I (again, hopefully) start my PhD and I'm confident it can work out fine. Overall, I believe it's doable.
The best advice I can pass on if you decide to juggle kids and school is to watch out for the "since", it's your worst enemy. Specially if your spouse works full time. Since you don't have class today, since you've got flex hours, since you can work on that paper later tonight...you might end up with an overload of house and family errands (all of which get significantly more time consuming with kids). School = work and will probably be as demanding, if not even much more demanding, than a full time job. Don't let a flex schedule give you the illusion that you can be responsible for more than your share of house and family chores. Your research or your sanity (or both) will suffer.
I did way more pick-up and drop-offs, groceries, kid's doctors than I should at the beginning of my MSc, and ended up doing 14 hour days non-stop (not even to eat) to finish my thesis. All of which could have been easily avoided hadn't I not fallen for the illusion stated above. I can only imagine the risks in a PhD pursuit being even higher.
Whatever you decide: good luck!
"From a situation in which everyone writes, few people read, and even fewer think, only chaos can result." ROBERT SOMMER