Instant "film" today is of limited quality and size as I'm sure you're aware.

Fuji had been making the FP-100C film for the old Polaroid cameras, but they stopped that this year IIRC, or at least announced they were going to stop.

That leaves you with the smaller format cameras and printers. The cameras spit out prints, and the printers which are battery powered can take an image from any camera including a cell phone. This IMHO makes them much more useful than the cameras.

We used to use the small portable printers to produce on-site prints during a shoot for various purposes, and it gives a traveling photographer something to leave with the people they photograph.

They do have multiple features depending on whose product you go with, such as self-stick backing and different sizes. It really depends what you want them for.
If it's simply to have fun with the kids, anything will do, but keep the cost in mind as its not negligible. They are fun and serve a purpose, as long as you take their limitations into consideration.