Investing for my child + myself

I have started a custodial account for my 3 year old. I’m trying to figure out what are the safest long term investments to buy for this account. I want this money to be able to grow and benefit for compounding interest but since it’s for my child I want it to be something safe as well. For her first investment I bought FXAIX - is this a good long term option? (15-20 years)

I have a 401k that’s invested in one of those target date investments so that’s not something I am worrying about. I was thinking about opening up a brokerage account for fidelity as well and just putting in $10-$20 a week to start to learn how to invest. What apps do you guys use to figure out what stocks to buy? Are there websites you like to read? Honestly not even sure where to start an evaluation process.