One of the biggest problems is that, outside of early school, there’s no real way to practice social interactions in a safe setting. The only real option is jumping straight in. If you’re already slightly socially stunted, it can be very easy to mess it up. It only takes a couple of negative reactions to put someone off for a long time.
I almost fell into the same hole when I was younger. Thankfully I realised what was likely happening and worked on it. I’m still not good at cold approach social interactions, but I can at least now do it without screwing up catastrophically.
My experience with young children is that they can be incredibly welcoming, and accepting. Only a few tend to be like you claim. They generally want to be friendly and be liked.
Unfortunately, they are also still developing and learning social skills. They often can’t tell different and guarded from hostile. They will often reflect back how they feel they are treated. This becomes a vicious cycle.
It’s about 8-9 that things like clicks can form. Social skills explode in complexity. This is where most aspies begin to fall behind. It can be overcome with training and/or practice, but that gets harder the further behind they fall. By the time it’s obvious, catching up is HARD.