So far each new Apple financial product makes me research and re-evaluate my options. When they announced their credit card, I got into "cash back" (thankful that I did), and ended up always getting good percentages back on every purchase. Apple Card was a jumping off point for further research. (For those curious, I ended up with Bank of America Premium Rewards at Platinum Honors tier + Amazon 5% card, Target 5% car…
Fidelity and Vanguard have "core" positions (all money goes into these) that are yielding 4.4-4.7%. They're money market funds so are covered by SIPC insurance. If you're looking to open up something for your kid, might as well just open one up for yourself as well.
But you can choose to invest your cash directly into the high yielding money market funds by placing a trade.
The relevant tickets are FDRXX and SPAXX.
Do note that this is different than changing your core position.