The poll for uSwitch.com found 27% of under-eights have one of the gadgets, while 17% were aged between two and three when they first learned to use a touchscreen and 10% were under two.
Some 84% of parents bought technology for their children last year, spending an average of £462 each or £5.6 billion collectively, the study found.
The majority of the spending - £3.2 billion - was on gadgets for Christmas.
And more than one-third of parents (36%) expect to spend more on gadgets for their children this year, with 91% saying their children already own at least one games console.
Almost one-sixth of parents (16%) believe their under-16-year-olds are addicted to gadgets, while more than one-quarter (26%) say their children would feel lost without them.
Seven in ten parents (71%) limit the hours their children spend using technology.
The study also revealed that more than one in 10 children (12%) have racked up unexpected bills by making in-app purchases on tablets and smartphones.
USwitch telecoms spokesman Ernest Doku said: "The term 'early adopters' now has a whole new meaning, with today's kids knowing their way around the latest tech before they're out of nappies.
"Once the gadget of choice for high-flyers and tech fans, the price of an entry-level tablet is now under £100, making them an attractive and affordable piece of kit for the whole family. They can also make lessons, homework and bedtime stories both fun and interactive."