Baby Arthur's hair is abundant when Merlin shows the baby to Vivan, but when the women of Avalon dance, baby Arthur is almost bald, and in the night, he has his head full of hair again.
While Arthur is converted into a dolphin, he passes near a whale, but the whale and Arthur as a dolphin have moved long without proper frames before.
When Merlin found baby Arthur in the burning house, there was a sound of a baby crying, but baby Arthur didn't have any signal of crying. The only way the baby sound could have sounded is because Arthur was crying.