Moms of 2 under 2 - what do you wish you had known ahead of time?

Our son will be 18m when our second baby will be joining us in September.

I’m 20weeks and realizing how fast this pregnancy is flying by!!

What do you wish someone had told you before you before your 2under2 baby arrived?

About us- only have the one child who’s 14m next week. This second baby will most likely be our last. First baby is a pretty good sleeper in his crib. Considering graduating him up a big boy bed ahead of baby #2 arrival. (He’s a climber and also very tall/strong for his age so it’s a possibility he might be climbing out sooner than later and hope to avoid the bed transition the first few weeks with newborn) Also both will share a room fairly quickly (hopefully once newborn is 8-9w old like we did with our first).

Thanks for your advice!!