I'd say it's more like 1/3 of a cup. It's preety teeny. It does come with a standard single-serve applesauce cup and a milk, but I'd put it in the category of "large snack" for a 5-year old rather than a full-on meal.
My DD (3.5) ate one for lunch at the Pacific Warf cafe and gobbled it down. She was still hungry after she finished it, so she shared my bread bowl with me, and that filled her up.
I'd suggest making sure whatever meal you get has shareable side order, or to bring some hearty snacks like string cheese or granola bars into the park with you if you don't want to have to buy snacks in the park.
At some of the restaurants, it was the best kids meal option for my DD, even though it really was too small. We knew she would eat the whole thing, but we also knew she would need to share our meals with her or get her a snack sooner than normal.
Hope it helps!