The step up from PS4 to Pro was mainly a 4k output and a faster processor. On a small/med tv (where 1080p HD is fine for resolution) being played by a kid the standard one is more than fine.
All my PlayStation stuff over the years has lasted pretty well. The console you should be able to get second hand easily, if it’s been looked after it’ll be fine. Controllers you may want from new as they’ll have been sat on under a cushion accidentally at least a million times by now.
PS3 is a good shout, same rules as above. Me and my mates from the flat opposite are thinking about doing a whip round for a PS3 (we’re all on 4th or 5th gen consoles) as we want to play split screen coop games which you can’t get these days. Progress doesn’t always go forward with the expense gadgets etc. Could be fun for the kids.