Agreed, there is never the perfect time to have children - you just have to dive in and embrace the challenges.
I had my 4th child in my 4th year (I began my program with a preschooler and toddler, and had my third along the way too, then had my youngest the spring before internship). I was trying to power on through, but this was A LOT for me to handle

(plus dissertation, which is like a birthing a baby in it's own right), so I took a year off and worked on dissertation (which I still did not complete until after internship because data collection was S L O W). I have always had a ton of support from my mom and husband during my doctoral program (my mom would come up and live with us for months at a time), so I was ready to handle internship when I tackled it with the additional support of a nanny who worked with us full-time (I actually thanked her in my dissertation acknowledgements because the bond she developed with my kids is endearing & invaluable). On internship, I was at a VA site, which was the best deal ever because I was out by 4:30pm on most days (as opposed to some other sites that require you to leave when the work is done, 6-7pm), and could be home for our family dinners each evening.
I would recommend coming up with a plan but also not beating yourself up if that plan does not go as you wished. And when you do have your little bundle, remember that there is nothing more important than you and your bundle for that first month postpartum (at the very least) IMO, especially with the first baby. Plan to put your work aside then, because the work (dissertation, internship, housework, etc.) will be there waiting for you...when you're ready. Guaranteed.
And things do ebb and flow, and all the hard work should pay off when it's said and done. I'm satisfied with how it has for me, and that's a good, intrinsic feeling.
Good luck!
