Pretty much the same as @spacelab.
"My parents gave me a first name that they have NEVER used, I have always gone by my middle name, I've never really asked why they never used my first name but they just didn't. Apparently even when I was a baby they introduced me with my middle name and everyone just accepted it.
I also hate my first name, it's not that I'm not used to it but it's just I actually really dislike it. It's a very average name and I've never identified myself with it. My middle has always been my identity, even to the point that people are surprised to find I have a first name when they somehow manage to see an ID or when we were in school. It's only an issue sometimes because usually strangers will call you by your first name (mostly teachers, doctors appointments, etc) but there's also plenty of times when people will ask which name I prefer and that's it."
My name was something ordinary followed by an unusual name, so it looked like a middle name - think something like Julie Cassandra (but not). I hated the first name although it was ok on others. It would only be used at things like appointments and by a teacher I disliked. It had no part in my identity and I changed my name at 18.
My siblings had proper middle names to honour relatives.
What made it worse was that my father found it amusing that I hated it and would tease me. Bullying.
If I were you, I would change the birth certificate before he is a year old.
I noticed that colleagues would sometimes have had e-mail addresses and usernames allocated by full name, so [email protected] not [email protected].