Going from having no kids to all of a sudden being responsible for a human life is a huge transition. After the first few initial months of worrying if every move you make or even worse, don't make, will somehow create a butterfly effect that'll result in the death of your offspring, you start to settle in the role of parent.
You expect the unexpected, you are bestowed new reflexes and situational awareness to break their fall or stop them from toppling onto their heads. You create a routine for them and help them stick to it. You manage to get some date nights with your SO and you find that adjusting to the life of a parent wasn't only just doable but actually pretty awesome.
Then you have baby number 2 and think to yourself, "Oh, I've got this parenting thing on lock what could possibly go- OH MY GOD!" Yes, as Jim Gaffigan so eloquently puts it, having another child is like you're drowning and then someone hands you a baby. It's not easy raising both a toddler and infant at the same time. It requires patience. Grace. And most important of all - a sense of humor.
So judging by these Chrissy Teigen tweets, she's more than ready to take on raising a second human being.