I can tell you my journey - at least as it relates to my son anyway.
He was born in 2003. I've got a pic of him in his bouncer holding a PC keyboard. One of his toys as a toddler, although my wife had me cut the cord short. At 3 he was sitting with me when I was working on a 6500 that
@bunnspecial now owns.
For a while we had a crap PC that I loaded up with games I got at the Goodwill (that's a good, inexpensive resource). When he turned five I gave him his own iBook. It was a low end G3 with a bad Airport antenna. The point was to teach him respect for his stuff.
Until he was about 14 or so we regularly hit up Starbucks and other coffee shops with our Macs. I'd run an ethernet cable from my PowerMac to his iBook and start Internet Sharing for him. Mostly the sites he went to were Nick Jr and such. Lots of online games for kids.
At some point I got him his own TiBook 1Ghz. I had to replace the screen though. Cost me $25. A 802.11n PC WiFi card was purchased for him because the original Airport Card in that Mac could no longer connect to Starbucks network. The Ti-Book was later replaced with a 15" PowerBook that had a bad ram slot.
After one particular incident with a next door 'friend' and snapping off a key from his iBook, my son started taking seriously the care of his tech devices.
Ultimately, this all won my son a brand new iPhone SE in 2017. I replaced that with a brand new iPhone SE 2020 a few months ago. He takes care of his stuff and I've never bought my kids any of the latest or greatest. My wife an I have a rule - the kids don't get better stuff than what we personally use, unless they pay for the extra themselves.
Both my kids only got phones when things developed that we had people in the house going in three directions. Kids to school, wife to school, me to work. We needed to be able to get a hold of the kids. My son was no older than 13 when he got his first phone, a iPhone 4s 8GB I paid $20 for. He was limited to a 2GB line and because of the 4s, 3G data.
My daughter was a bit younger, but it was an iPhone 5 she got, 2GB line and limited to HSPA+.
Let's just say my daughter is still stuck on an iPhone 6s because she hasn't learned the same lessons her brother has.
Anyway, lots of stuff out there. For baby's/toddlers you might look into AlphaBaby. It's an app that locks out everything while running (special keyboard command to escape). It shows on screen whatever key is pressed and says that key out loud. My son and daughter had a few rounds of that when they were that young.