Can
a Muslim sell products that he has purchased wholesale having a price
ready-printed on them (e.g. canned drinks on special offers) at a higher
price to others, in particular to Muslim children?

Praise be to Allaah. 

There is
nothing wrong with increasing the price, because this is what trading and
business are based on. But there exists the condition that this should not
involve lying, cheating or hoarding something that people need, such as
food staples, etc.