My DS will eat a big breakfast but then really just eats small meals/snacks throughout the day. He is also very active and I make sure he gets lots of exercise.
For example, he had eggs with avocado/cheese, yogurt and fruit for breakfast. Around 11:30am he had trail mix, for lunch part of a half sandwich and he was full, about 2pm a handful of carrots with dip=full, 3:30 he had a banana and milk=full again. For dinner at 6pm he had some pasta and veggies with the rest of the family but only about 8 bites. At 7:30pm he wants maybe a few bites of a fruit bar and milk. Not a lot of food at each sitting but because he is eating throughout the day, I don't worry about it. Plus his pedi said not to worry.
My son is 41 in tall and 36 lbs; tall & lean.
Just keep offering what he likes for right now. As he continues to get older, he will want to try different things.
If he’s hungry he’ll eat.