My DD has always been a fast learner and apparently is a fast developer. By 5 months she was sitting unassisted, she can wave, say some words, had two teeth at almost 6 months and has great hand/eye coordination... But she shows little interest in crawling, she will now stand up a little when held onto and she's only just learned how to roll from front to back. She can't roll back to front. If I put her on her tummy to encourage crawling she just rolls back over or cries (she's always hated being on her tummy). Is this normal?