Transitions are tricky, and there is much debate regarding which family size transition is hardest...zero to one, one to two, two to three, three plus. While I have no experience with the zero to one category, I can tell you that there is definitely a difference when you go from two to three.
For the first time, you are constantly outnumbered, even when both parents are present and engaged. This can lead to some questionable public restroom and parking-lot-crossing situations.
You can no longer have passengers in a regular sized car. Our family of five now fills our SUV to the brim. Need a ride? Sorry.
You are forced to be more creative. From stroller/carry/walking combinations to get through the mall to how to fit everyone around a table made for four, adding a third little one creates some life riddles.
You don't get invited to people's houses very often. You think you and your two kids are unwelcome guests? Just wait until you add a third. I cannot imagine why allowing three children three and under to roam through your beautiful home is not appealing. Seriously, though, your invitations come less often....but your life-long friends will still allow your army to invade their turf.
Twenty minutes. For us, at least, the difference in two kids and three kids appears to be 20 minutes. Pre-kids, we were early to everything. With the twins, we were typically right on time. Now, we are almost always 20 minutes late. To everything. I have become one of those chronically late people that used to drive me crazy. But somehow getting those final items in the diaper bag and three pairs of shoes located and on feet always takes longer than planned.
You have even more fun than you had with two kids. Although it can be work, watching three kids play together is amazing. I love the moments I can sneak into the playroom and see them all working hard in their kitchen. And with three kids, at least one of them always wants to play with you. More playmates for everyone.
Your life is even more full. I have a theory--the messiest lives are the fullest lives. Nothing against people that have it all together, but I truly believe that there is much joy to be found amidst chaos.
You love even more than before. You thought your heart was full when you married. Then you had your first (two) kids, and just knew your heart was at the brim. Somehow, though, with that third, your love just keeps growing. God gave us an incredible capacity to love. And adding our third little one truly unlocked that capacity a little bit more for us.