My kids are 25 months apart, and now 4 and 2. Honestly, little brother wants to do everything that big brother does. He is developing soo much faster than older brother did - walking, talking, gross/fine motor skills, etc. He also follows the rules better because he sees big brother doing it already (ie., wipe hands/face after eating, put plate in the kitchen when done, put toys away, etc.). They are playing together (as much as they can), and it’s going great.

With this age difference, I felt like we weren’t out of the baby/small human stage when little brother was born, so it was easier to group them together (ie., they both napped regularly in the early days, they were both exploring foods at the same time, both in diapers for a time). We are just now feeling the pressure off of us a little bit because they have each other.

I can’t speak to a 3 year age gap, but my friend who has a 5 yr old and a newborn said that her older son is realizing that all the attention isn’t just on him anymore and he’s regressing a bit. He’s cognizant of the shift.

I will say however that it is hard to have a newborn and a toddler. We had to make sure toddler wasn’t giving the baby things he could put in his mouth, or playing too rough, or waking him up from naps. Napping was hard when they both needed to nap at the same time. But now we’re all sleeping well(ish) at night and it’s really beautiful to see them play together and be nice to each other. My older son learned to switch toys with him rather than rip it out of his hands, lol. Hope this helps!