Logan felt to need to tell the others that he regressed. After all, he could always take care of himself. That was not an exaggeration, or a lie so he did not have to communicate. He really could take care of himself. After all, there was very little in the form of taking care of oneself that Logan at thirteen could not do on his own.
And that was another reason he did not mention it.
The sides besides him that regressed all became young children. They needed care and attention at a level that was understandable and more than okay. However, it was not what he needed. If he told the others he regressed, they would assume he became a young child, and would almost certainly be disappointed that he did not become a child they could all coo over.
So he chose, by himself, never to mention it.
(That did not mean regressing without anyone else aware was at all less difficult.)