Professional advisers that are free to you are paid by the "products" they have to offer and are very biased towards their own earnings. I have had a few bad experiences with the recommendations these advisors make that benefit them more than me.
You pay fee for service advisors and therefore they are less biased about the investment options they recommend. But they are very expensive related to my assets and certainly the funds your kids received.
I recommend investing those funds on your own. The 529 plans are educational for kids in that they list the investment option you have chosen, the unit price, number of units held, etc so you can track the growth of their investments. The 529 does have tax advantages not available through other investments and the funds can be used in a variety of ways.
I agree the other investment option is a CD but rates for those are low right now too.
A savings account is also a good educational tool for kids when they get a bit older.
Good for you for being so thoughtful about those funds.