I say this because the kids were absolutely over the moon when we would stop for a break at a cafe that served Croque Monsieur (ham and cheese toasted sandwich only better).
I was first introduced to these delectible sandwiches in Australia at a french inspired cafe (in a foodcourt no less). I love that there is a beschamel on the top and it goos out when you eat the sandwich. Not so good if you are watching your weight (stay away from this one). But for the kids it is great and cheap from the fast food cafes in Paris. There is also Croque Madame which is basically the same but with a fried egg included.
Yummy! My 2 sons had one everyday for breakfast and were hardly ever complaining of hunger for lunch, they cost about 3-5 Euros with juice at a cafe.