Informal education can take on many manifestations. People learn in almost every area of life, from watching television to playing with paint and chalk. For an activity to qualify as educational, I think, we only need to see some teaching intent.
If a parent sits down with a child and suggests that the child mix colors in a painting exercise to see what new colors are created, we are talking about an informal educational exercise. When the painting activity is not at all directed by the parent, we may be talking about a potential learning opportunity for the child, but not an "educational" one.
Formal education is some kind of organized schooling. Informal education is the learning that people get from parents, peers, and other influences. Finally, non-formal education is the kind of education people give themselves, such as reading books.