I don't know FOL, but hopefully I can help you solve the problem.
1 ■ Huey is younger than the boy in the green tee-shirt.
2 ■ The 5-year-old wore the tee-shirt with the camel design.
3 ■ Dewey’s tee-shirt was yellow.
4 ■ Louie’s tee-shirt bore the giraffe design.
5 ■ The panda design was not featured on the white tee-shirt.
Statement 1 implies Huey is not wearing a green shirt. Statement 3 implies he's not wearing the yellow shirt. Hence he's wearing the white shirt. Then 4 and 5 imply that Huey's shirt bore the camel design. Statement 2 implies that Huey is 5. Hence: Huey, 5, white, camel
By Statement 1, since Huey is younger than the boy in the green t-shirt, this implies that the boy in the green shirt is 6. Hence by Statement 3, Louie is 6 and Dewey is 4. Hence: Louie, 6, green, giraffe. Dewey, 4, yellow, panda.
It's a bit confusing at first, but if you work it out you should be fine. A table can help as well.