Each stanza seems to represent a different moment of worry for the parent. The 'mystical machines' could be planes, the alliterative description suggesting that the experience of flying is alien to the parent. The worry perhaps comes out of the parent living a sheltered life and being scared of the 'mystical' things the child is experiencing. She fears that the plane will crash and longs for the child to be in a place of safety: 'safely, safe home', a refrain that is repeated at the end of each stanza.
The photograph 'in the fridge' is a strange image, perhaps suggesting that the parent wants to regularly reminded of the child and feels cold without them there. They fear that they will be 'burnt in the public places' which could be a simple fear of sunburn, but the image also evokes horrible torture which could happen if the child takes their adventuring to a hostile place.
However, the being set on fire argument is perhaps redundant when the 'hole in the sky' is referenced in stanza three. This image refers to the hole in the ozone layer and the parent hyperbolically describes sunburn as being 'gnawed to shreds' - an example of the parent's over-the-top worry. The parent is keen for regular contact: