"No, because..." is what I have always used. "Liebling, do not run around when Mamma has a hot drink. If you bump the drink it will spill and hurt someone." It is longer to say than "NO!" but he knows why I have said no so respects it more than a straight "no".

To add to Santosha, I find that distraction works well too. "Liebling, can you help me push the trolley and find the food?" That is better than "don't run off" because he is engaged with the shopping.

All else fails, I just say "meow" and DS stops what he is doing to play with the "cat". But Palmer may be a bit young for that.