Flying with infants.

I'm taking my 7 month old son on a cross-country next month. He's flown on
an airline before and he handled it quite well.

I'm worried about hearing protection. Should I even bother? Would regular
ear-muffs be enough for him or should I find some infant-sized hearing
protection? How about those headsets you wear when shooting rifles?

I plan to have mom sit in the back seat with the baby and big brother will
help fly the plane. Anybody got any other advice?

Thanks,
Alex