I would only sell the disposable vapes in shops that sell tobacco products and shops dedicated to vaping. Not sweet shops. Not Poundland. With dedicated vaping shops, my friend was in one and 3 kids tried to come in and one of the workers said "you need to be 18" to them and they left.
Plus get rid of the colourful packaging. Some vapes I have seen are black with different coloured writing on them to match the flavour. That would be acceptable. Another acceptable way - again seen the vapes whilst wombling - a simple symbol(s) of flavours.
This has just crossed my mind as well, mental how basically anywhere can them when tobacco licensing is so strict!