Is it possible to have an Apple watch with a phone number and pair that with an iPad Mini and not have an iPhone involved at all? My daughter is getting old enough to need a phone but she is ADHD as all get out and will most likely put it down and lose it. So I like the idea of a watch that is strapped to her and then an iPad Mini for when she needs more.
The technical reason is battery life. The battery on an Apple Watch is about 1Wh - which means it can probably only power the CPU for about 20 minutes before the battery will be flat.
The only way to get all day battery life out of the Watch is to divid your ~20 minutes of CPU time into several hundred very short bursts that need to last less than a quarter of a second. Apple does that by outsourcing most of the Watch’s compute time to the iPhone that it’s paired to which is almost always going to be in your pocket or bag and within bluetooth range.
An iPad is never going to be within bluetooth range all day long every day. Nobody takes them with them everywhere.