The Sesame Street Food Trucks "area" is a great looking, well themed counter service location — that is a little confusing to me, but I'll tell you what I know.
There's basically three kiosks/counters in this area ... ABC Eats (the green truck) which serves several varieties of chicken tenders ... Sesame Sips (middle, large counter area building with a green vinyl awning) which serves smoothies and slushy drinks ... and Yummy Yummy Nom Noms (a blue, purple and pink truck) which offers a couple of grilled cheese sandwiches and chicken tender meals.
However — I've only seen two of the three locations actually open, (the main counter building and the blue and purple truck). It also looks like the "ABC Eats" and the "Yummy Yummy Nom Noms" menu are now identical (they were not when this area first opened).
I'd recommend going to the main counter (building) first and ask them where you order something ... unless you see a line of people that look like they're cueing up for food — if so, they probably know what they're doing. This location is not usually part of the All-Day Dining Deal and is often referred to on actual SeaWorld printed material as "Eats on the Streets".
(*) Price ranges listed are the average cost for one main entree and one soft beverage item, unless otherwise stated. There are many combinations of appetizers, deserts and drinks that will add to your final total. Many parks also use seasonal pricing systems which result in food and beverage costs increasing at peak times. Please check with the location that you are interested in for specific pricing information.