cracked paint

[kittycats]

My daughter has just painted her bedroom but the paint on the walls is cracked.

The same paint and brush was used on the ceiling first and thats ok so why is the wall paint cracked?

It probably means that the pain underneath is different on the ceiling to the walls and whatever was on the walls hasn't provided a proper key. I know if you paint gloss onto matt emulsion rather than primer or undercoat it blisters and cracks - don't know what other paints don't go together.