Yes you can use it for painting, if it's a bit strong just dilute it. It depends on how sensitive the skin. Don't apply it at full strength on sensitive areas or it can burn. You could also use it mixed with coconut oil.

There are a few mothers here who can help you with young children . I haven't used it for a child that young so best ask them and read the past posts. You wouldn't need to give a 6 year old much

If you're buying the 500ml bottle then get some 30ml brown glass dropper bottles from a chemist too and put it in them
Best use a small funnel to avoid spills

There's plenty of good info in this forum. You need to get companion nutrients like selemomethionine too
Read the faqs too and use the search for anything specific