At that age, no, assuming the food is nutritious. When they are older, depends on the kid. My daughter in all her 8.5 years has never once told me she's eaten too much and felt overfull and/or sick. She self-regulates really well even with special-occasion sweets and treats. I almost don't even monitor her.
My 6 yo son, otoh, tends to overeat if he really loves something, though he is getting better. I monitor him more closely and if I become concerned about the amount he's eating I'll ask him if his tummy is full. Then I'll remind him that I can save whats left on his plate or an extra portion for him to have later. Sometimes that prompts him to stop, sometimes he keeps eating.

I still let him decide for the most part. It's just that sometimes with his favorite foods he seems to want to know that it won't all be gone later if he doesn't eat all he can now.

For both of them, though, I do require that nutritious food is eaten first before the "fun" stuff, unless it's at a birthday party or something like that.