End of primary school they had a phone each (year 6). They made their own way home in preparation for secondary school.
They had Amazon tablets from 8y (junior in primary school) although seldom used as they preferred playing with their toys/games & loved being outside come rain or shine.
Currently the 12.5y old intermittently uses his phone (good at texting family not fussed about the apps) but plays his games console. No tablet/iPad. Not interested.
His 15y old sister is the same with the phone use (great at using it as an actual phone, doesn't use too many apps) albeit replace phone with iPad/TV time.
I would let them play on the 'family IPAD' as a treat/game like you would when you play another game/activity with them, just to keep them up to date with tech but there is no need to have their own too early.
~ 4/5y is too early in my opinion, however when my son got his at 8y, he became a little frustrated as everyone knew what to do in the tablet/tech IT sessions in school, and he was still learning/inputting stuff when others had finished. It's hard to avoid when schools use them as part of teaching!
Saying this, children need to explore role play, interactions with others via games/puzzles and importantly imaginative play for several years for optimum emotional, analytical, creative and social brain development; they can't get this from a tablet.