This is a 1988 vintage Teenage Mutant Ninja Turtles shirt. Yes it was mine as a kid. It does not have a size but would likely fit a Second to Third grader if they are about average size.
The colors on the turtle are vibrant and look awesome. There is some staining on the back and a few small spots on the front. This has the official TNMNT tag inside. This was produced by Mirage Studios in 1988. 90% or more of the vintage shirts on Ebay are from 1990 forward. It's one of the oldest TNMNT shirts you can get, and the only one on Ebay. Very rare! It would make your little one look like a rock-star!