We often underestimate the ability of our children to understand our true motives. In fact, we can always tell them the truth. We can explain to our child why these foods are harmful and that they need to eat real food to be healthy and strong. Persuasion always works better than prohibitions.
Don’t be too extreme in your restrictions. If your child really wants to try harmful food, let them. If you don’t, then one day they will want to satisfy their curiosity when you are not around. They will lie to you, hide and feel guilty. The goal is to make healthy eating the child’s choice. The occasional consumption of harmful food will not harm their health but will give them a sense of freedom to choose, to decide what to eat and what to buy. Children who do not feel free often break the rules and develop a particular obsession with forbidden things.