I have a three year old and a six year old now, and a company that's only seven years old. I thought long and hard about what it took to be an entrepreneur of a new company along with a dad and I've definitely learned my lesson(s) over the years.
My biggest tips would be to make your workflow and business as mobile as possible. When my first daughter was born in 2007, the iPhone was brand new and the world of apps and even web apps that were functional on mobiles was pretty nascent. Over the years, that's definitely improved and I still gravitate towards services and products that allow me to run my business from my phone or tablet in the middle of ice cream runs or school pick up lines or doctor visits. Additionally, I was the only employee of my company at first, so it was easy for me to hunt and peck the right apps. But even in recent years, we've shifted our company to be very heavily focused on Google Drive and recently Basecamp because of their great integration across mobile platforms.
If you have employees or partners, lean on them and they'll be glad to help. If you're flying solo, look for ways to streamline your workflow and production process.
Of course, you don't want to be that dad at the soccer game or pre-school info session etc that's constantly on his device rather than being there in the "real world," so you have to really make sure to not let work and being an entrepreneur be your time stealer away from your kids and family as they'll need you more than ever in that first year and in the years to come.
It's hard, but it's worth it. My startup and my kids have grown up together. While my kids come first, they already recognize that "daddy's business" is a big part of our family and respect what I do because I made time to include them early on and engage them as much as I could in the work I was doing.
Good luck, and have fun... it's an amazing experience to be a simultaneous entrepreneur and dad.
TL;DR Don't be Don Draper.