TVNZ had advertising-free preschool hours on TV2 on weekdays between 6.30am and 6.55am and from 8.15am to 9am, and on weekends from 6am to 7am.
MediaWorks runs its ad-free programmes for preschoolers on Channel Four from 6am to 7am, 8.30am to 10am and 2pm to 3pm on weekdays.
TV One and TV3 do not have any designated programming for preschoolers.
Survey lead author and marketing lecturer Dr Leah Watkins said a lot of advertising in the peak preschool viewing times of 7am-8am and 4pm-5pm was clearly aimed at preschoolers, even though the shows screened at those times were supposed to be for older children.
"They're advertising Doc McStuffin products, Little Tikes, Peppa Pig Playhouse and Transformers," she said.
"My 3-year-old is into the Transformers. Primary-school-age kids are also into the Transformers, but clearly some of this stuff, like Lalaloopsy dolls, primary school kids wouldn't even be interested in."
She said the TV companies' "self-industry regulation is out of step with the reality of preschoolers' viewing pat-terns".
"Arguably it's quite deliberate. They are relatively ineffective, but they can argue that they are being proactive around these issues," she said.
Her survey found that most preschoolers watch TV more than the American Academy of Paediatrics guideline of no screen time before age 2 and less than two hours a day above that.
In the survey 75 per cent of under-2s watched some TV, and 39 per cent of 3-year-olds and 55 per cent of 4-year-olds watched for two hours or more.
But TVNZ head of television Jeff Latch said there were still tight controls governing advertising screened during all children's shows.
MediaWorks communications manager Rachel Lorimer said: "We always err on the side of caution when it comes to content.
"For example in the afternoons, the first half of Sticky TV runs without ads because it includes programmes like Dora the Explorer."
What preschoolers watch
Weekday peak 7am-8am
TV2
* The Looney Tunes Show
* Spongebob Squarepants
* Beyblades Metal Masters
Channel Four
* Sticky TV
* The Wild Thornberrys
* Rugrats.