It's for my niece. But I am the odd duck going through shit so I could probably get away with the unshaven, trackie bums and stained t-shirt. I may as well milk everything I'm going through.
Suit and tie or dress trousers and contrasting blazer, possibly tie? Preferably not black.
Mind you, last time I went to a christening was in the nineties.
You could go a bit formal suit and tie. I’m just going to go in smart casual though but I think from memory last time quite a bit of the family dressed up very big for it.