Legal Question: Can a Store Ban Backpacks?

Questioner

There is a 'shop' near me, recently I went there to do my shopping as usual (I had my backpack on because I had cycled here and could easily take my groceries back with me after purchase). Once in the shop I was suddenly called by an employee of the 'shop', asking if they could look in my bag. At first I was surprised but I just let it happen, the employee apparently did not find what he was looking for and gave my bag back and asked if I wanted to put it in a locker, I asked why in surprise and was told that schoolchildren are not allowed to take a backpack into the shop. Apparently this was also stated somewhere which I unfortunately overlooked. My question now is, is the 'shop' allowed to forbid a specific group of schoolchildren to take a backpack? I mean I understand that they are suspicious of schoolchildren and that they are afraid that things will be stolen. But as far as I know it is forbidden to discriminate against groups of people, isn't it? I mean older people should be allowed to enter the shop with a backpack, but if you are a schoolchild this is not allowed? Also, how do they know if you are a student or not? And besides, the lockers they offer are not exactly safe... So can they forbid you to do this? I would like to hear from you

Lawyer

Yes, that is allowed. A shopkeeper may set house rules, such as this one with the backpack. These must then be clearly stated upon entry, so that everyone can choose: do I enter this shop and then also adhere to this rule or do I go shopping elsewhere?