529 for kid brother, or another type of investment?

My father re-married a much younger woman, so I have a brother who is 30 years younger than me. Today, he is six.

When I was growing up, my father was in a position to pay for my college education in full. I am doubtful he is able to do that for my kid brother. My husband and I are fairly high earners, so I am in a position to step in and help. While it's unlikely I could put together enough money to pay for, say, four years of private school, I want to put away what I can for him to at least make a dent in his educational expenses. (I am also trying to get pregnant right now and need to pay for my own kids' schooling.)

Is a 529 the best way to go, or will this end up hurting his financial aid opportunities either from the government or the school of his choice? Would another kind of investment vehicle be better for him (like making him an employee and giving him a Roth IRA or something)?

Here's the other kicker if it matters. I am estranged from my father (see above re: much younger woman) and don't have much of a relationship with my kid brother right now. I hope to develop one as he gets older. I don't plan to tell him or my dad about this savings account for him until he's much older, unless I hear otherwise for some reason I should.

Thanks for all your kind help and advice.