I think you should make the quilts now but save them until the kids graduate from HS. My thinking is: You're healthy now and able to make the quilts. While there's no reason to expect anything dire to happen between now and their graduations, there's also no guarantee.
If you make them now, you'd be wise to put notes on them to indicate your intended recipient. You'd also be wise to advise the parents of these nieces and nephews as to the quilts' existence and location.