This depends on where the other 80K you need is going to come from.
You might want to minimize taxable events (like selling assets for capital gains) until the second child’s first FAFSA is done, for example.
Or, if your income is low enough to claim a tuition tax benefit, you might want to pay some tuition out of income to take advantage of that.
I’m not sure why you would take any loan sooner than you needed to. 529 plans are considered parent savings for financial aid purposes already, so from a financial aid standpoint the assets are equivalent. Selling shares in a 529 plan for college does not incur capital gains tax, though, so these options are not exactly the same to the IRS.
Do not assume anything about future financial aid. Ask the financial aid office at child 1’s school what if anything changes when child 2 starts school. For example, if your package includes merit aid, the school might say you are already getting more than you “need” and there is no reason to increase your grant aid.