Funding 529 account for different aged kids

My wife and I have been indecisive about how to handle kid college fund management. We agree we want to cover most/all of college costs for our three kids. The plan so far has just to use money from our own investments to do that but recently we've been thinking about 529 plans again.

One "issue" is out oldest is 5 and our youngest is 1. I don't want the oldest to resent having 4 less years of growth or whatever. The plan is roughly to front load the accounts, so if we seed the 1 year old's account with $50k it will be $135k when she reaches 18, vs if we seed the 5 year old's account with $50k it will "only" be $105k.

Has anyone else dealt with this? What can we do to keep things fair?

Some ideas we have discussed would be to seed the 5 yo with $63k instead, to give the same mathematical return by 18. We also considered keeping it simple, identical seed amounts, and square up financial aid at the end from our own investments. We're open to any other ideas.