Android

Nokia still makes dumb phones now, with 4G too!

Check out the Nokia 225 4G and 6300 4G.

just putting it out there: giving them a cheap android phone will steer them away from android forever as they will be conditioned to think that all android are as cheap and terrible as the ones they have been given

Say no more, OP.
Rotary Un-Smartphone.

Google needs to make the three Little Pigsels, a series of special starter Pixels for children. The three Pigsels come in Straw, Wood, or Brick, and feature a stock Android UI and a standard Pixel camera to get your child started on the correct path.

I‘d also go the parental controls route, you can relax that gradually as they grow older instead of having to buy new phones.

If you have any of your previous devices laying around, there you go. Otherwise you can always purchase the cheapest of the cheap like a $30 walmart phone. Data and apps can be limited but at that price point internet might be so frustrating to use that it's a deterrent as is.

You could go this route. The phones have good various parental controls, relatively cheap and effective. Gabb Phone

I've seen kids with smartwatches as a solution to this

If you're truly just after 911, Even a deactivated cell phone would call that in the US.

We ended up getting the kid an Apple smartwatch with LTE. The monthly price when it's not bad it's like 10 bucks. The upshot being he could call us with it we could call him with it and find my iPhone can locate him at any time.

I bought this one for my youngest brother. It works fine and it comes with a years worth of service. Bought it so he can call me during emergencies. https://slickdeals.net/share/android_app/fp/829226

Lowend Android phone with parental contols and no SIM wouldn't work?

Do you still have an old android phone sitting in a drawer somewhere? Perhaps giving the child this with parental controls might be a useful solution. My rationale

1. You can still use an app such as Signal or WhatsApp to communicate with them. These notably support encryption unlike SMS
2. You can also use "find my device" (relevant android police article on this topic)
3. This is cheaper than buying even a cheap dumb phone since you already own the device, and you can argue better for the environment since you're re-using something instead of creating more e-waste
4. Particularly if the Android phone is still updated, it is more secure than a dumb phone these days.

I got a gently used sonim phone for $50 on eBay, they have industructable feature phones with great battery life.

Any phone would do just that. Get the cheapest dumb phone you can find. That way it also doesn't break the bank when it eventually breaks.

Plenty of basic flip phones available for cheap, Tracfone has a Nokia for 20 bucks. Could look at phones targeted for seniors, like the jitterbug flip, if they're really young but that would be more expensive than a basic flip phone.

Just search dumb/bar/feature phone on Amazon, you'll find lots of it. If you want 4G connectivity, add 4G keywords. That's it.

I would say go with an older Apple phone. Their stock parental controls tend to be a bit better than what you can get on Android without modding, and (let's be real) it will probably be supported for longer. When they get older you can disable the features to their maturity level.

Kyocera DuraXE looks promising, but not compatible with all carriers.

some traditional smartphone functionality would be useful for a kid - maps, for example. no idea if there's a partially dumb phone out there.