I would think shop assistants have enough to do in their own job apart from intervening with children. It is up to the parent to control their child. My 3 yr old son gets 'overwhelmed' in shops, so if I need to shop, I go directly to what I want, purchase it and leave. I also tell my son that this is what is going to happen. If for any reason he starts to 'act up' which generally is to run off, then I leave the shop immediately. This can be a real pain, especially as I don't get to buy what I need but it is better than the saga of having a naughty child in a shop, for all concerned.