Here's a question for you - do you rate this higher than superficial 'pretty' work by an adult, because the child is painting with purity and instinct or less because she's only a child?
Credibility is the only currency worth anything in art. Unfortunately, children don't have it and neither do many adults if they're crazy.
It's ironic how if you had no idea who a painting was by and whether they were 5 or 50 years old, or wearing nappies or straight jackets; you would not be able to say whether it was better or worse because of it. Yet once we know we're all incredibly quick to pass judgement.