Early diagnosis of any issue is always better as early intervention can help kids develop skills in their areas of weakness more easily. It might be ADHD or might be something else. I don't think 4 is to young, if you have someone assess that specialises in younger children.

You really have a lot going on though, so I'd do what you can in your own time Xox you're kids are lucky to have a mum who thinks so carefully about her kids Xox