Broken glass is rarely the risk that people who hardly ever go barefoot seem to think it is.
Healthy bare feet are a lot more durable than most people realize. As Steven E. Robbins states in an article in "Foot & Ankle":
"Another aspect of barefoot safety is risk of puncture wounds. A report has shown that when the plantar surface is subjected to localized load via sharp deforming objects, it deforms so as to contain the object in the void created by the deforming object, thus resisting perforation. Whereas the risk of plantar surface puncture wounds must be greater when barefoot if compared with wearing shoes, this skin defense makes the sole of the foot reasonably resistant to penetration."
A more complete extract from this article is available here.
In some parts of town, there will be sidewalks where you see a few flecks of broken glass. Older children and adults can be taught to navigate through stretches of this with minimal danger. As long as you never drag your feet and step down carefully, problems are unlikely. Even if a small splinter "sticks" to the sole .. it's normally quite easy to pull off. Usually the skin isn't even broken and even if it is, such tiny wounds will seal quickly. Of course, you aren't going to want that to be anything more than an extremely rare occurrence. If there really is too much glass (or more than a short stretch), go around it or put sandals on. Smaller children can be picked up or led around these hazards. Older children soon learn (with only a little explanation and encouragement) how to cope in this situation. You will also get to know which streets and areas tend to have this hazard. Please don't scare your children by exaggerating this hazard ... but show them how to respect and cope with it. We often hear parents say that their children must wear shoes all the time because "there might be glass". To us this is an over-reaction to a risk which, while real, can certainly be managed.
But, What About ...