I'm noticing several people talking about the ability of the parents to cope, and that's a factor, too. I consider ds2 to be high needs (technically, I think he's still-undiagnosed SN, but that's similar from a coping standpoint). However, there are definitely much higher needs children around! While there are days when I feel as though he's the most difficult child ever, I'm totally aware that that's not even close to being true. However, I'm also not getting enough sleep, and at this point, my sleep deprivation, fatigue, etc. can be measured in years (with a few short periods where I got enough rest), not months. I've been anemic through all of my last four pregnancies, and was severely anemic after we lost Aaron (high blood loss, although I didn't require transfusion). I've had a lot of issues (PTSD and depression) around my multiple c-sections. I've had a long, hard haul to get back on my feet after we lost Aaron. I have long-term nerve damage in my pelvis (dates back to the c-section when I had ds2), as well as a severe diastasis, both of which affect my physical well-being in a variety of ways I strongly suspect that I have some kind of thyroid and/or adrenal issue going on. So...ds2 is a handful, and would be a handful, no matter what. But, he probably wouldn't be as overwhelming to someone with more energy, both mental and physical, than I currently possess, yk?
Parenting was a whole different ballgame when I had ds1...I was only 24 when he was born, and hadn't had quite the reproductive butt-kicking that I eventually experienced. I just has SO much more energy. (I often feel that I've been tired since I got pregnant with dd1.) These things do make a difference. When someone says their baby/child is high needs, I don't think of that in terms of "that kids seems so much easier than dd1 as a baby!". I think of it in terms of how much the baby/child needs vs. how much the parent has to give. That's really the key equation, imo. If a child needs more than the parents have to give, then that child is going to be "high needs" for that/those parent(s), even if another parent wouldn't use the same terminology.