My children generally don't over-eat. After school is the time they are most interested in snacking. If I see the kids continually getting food out of the fridge or cupboard before dinner I will say something but this usually isn't a problem.
If you are concerned about snacking at inappropriate times it's possible to put some food out only during the times you would like or allow the children to access the food.
There are so many advantages to my children being able to access their own snack. They decide when and what (within a range) to eat. They learn to self regulate their food intake. They learn a whole range of skills like pouring, peeling, scooping, cutting, opening packets. They learn grace and courtesy, especially when we have guests. And for the most part they don't need to ask me for permission or help.
Allowing the children to safely and within reason access their own snacks gives them confidence and empowers them to make decisions about their own being.
In the children's fridge there is currently milk, yoghurt, cheese sticks and fruit (strawberries, grapes and cherries). In the pantry cupboard there is more fruit (banana and apple), wraps and nuts.
Keep in mind that if they can access their own food it's also a good idea to allow them access to an apron, glasses, plates, utensils and some clean up tools like a dustpan, bucket, mop, cleaning cloths and a compost bucket. A low clear and clean working surface such a small table is also a good idea - generally the children need somewhere to work and get their snack ready. These are of course not essential but they help the child to complete a cycle of preparing the food, cleaning and packing up.
And just because I caught a few images of Otis (with full supervision and some guidance) making after-school snack for Caspar.
Grated cheese and spinach in a wrap, cooked on both sides on the electric skillet (found here).