Board Thread:Questions and Answers/@comment-33790467-20190814010218/@comment-995426-20190820052802

There are methods to determine gender, but not to the untrained eye, and not when turtles are still young. And honestly, it's not difficult to imagine that Splinter may have initially been uncertain about their gender, and may have given them tentative names, or even waited a while before naming them.

But this whole thing could just be one of those "acceptable breaks from reality," like, for example, similarly glossing over how Splinter and the Turtles have a fully-stocked kitchen despite none of them having a job and none of them finding it that easy to shop for groceries.