A snack close to dinner
A snack right before dinner often means they sit down already full, or already frustrated. Leave a gap you can live with.
Leave a gap
If they are truly hungry, offer a small piece of a food that will also be on the dinner plate.
A banana at 5:30 and a banana on the plate at 6 is one food doing both jobs. A cupboard graze at 5:55 is a different dinner.
Hunger versus habit
Some asking is the clock, not the stomach. A small piece and a drink of water can hold the gap.
If they are shaky or unusually upset, feed them. A miserable wait is not a lesson.
What dinner becomes
If the snack was huge, expect a short dinner and do not take it personally. Serve the familiar food anyway, in a small amount.
Tomorrow, move the snack earlier if you can. The gap is a household choice, not a moral one.
A sentence you can say
“Have a piece of the banana that will be at dinner.”