The fact that children take a long time to learn thier own names is not surprising. Most parents I know are calling their kids all sort of names. Words they are using might be related to the actual name or not. Like all those honeys, dears, sweeties, etc. Taking all non-related words out still leaves a bunch of variations. Here are a few we use for our son:
Maxim, Max, Maxik, Maximushka, Maximka, Maximchik, Maximus, Maxut, Maximillian, Maxy, Maxo, Maxishe…