Um, perhaps by calmly asking them to explain what they are doing and why? By removing them from the restaurant and dealing with their behaviour in private, rather than infront of a bunch of strangers? As a parent, I think I should be the one feeling embarrassed because clearly I had stuffed up along the way. Embarrassing a child is not necessarily going to improve their behaviour, but is highly likely to lead to further issues (such as a child rebelling further etc.).