My cousin had a son who was only diagnosed with autism at 8 years old even though the signs are visible since he was 2. He started off like a normal child, he even called "mama" and "papa" but at one point of time, he just stopped calling them. This was their 2nd child but 1st son and they were in denial. They already had a daughter and already understood all the developments milestone for a normal child but they kept reasoning that because he is a boy, his development is slower.
They live in a different state from me, so I could only point them to the nearest NASOM centre when they finally come to terms with it.