The brightly coloured Firefly handset has five buttons – two of which call mum and dad directly.

The Dublin-based firm behind the invention plans to launch the phone in the UK by the end of the year.

But there were warnings that gadgets like this were 'eroding childhood' and concerns have been raised about youngsters being exposed to radiation.

Details of the new Firefly phones, which look more like a toy than an actual working phone, came about as figures show that more than half of children under 10 now own a mobile.

Over 7,000 of the £85 handsets have already been sold in Ireland.

Mum-of-three Jackie Douglas, 30, from Marsden, said: "It's ridiculous for a bairn as young as four to have a mobile phone. These days they're making kids older than they are.

"They should always be in sight anyway. You don't leave a bairn on their own do you?"

Husband Stephen, 32, a CCTV operative, added: "It's a good idea for kids around eight or nine years old but they wouldn't want one with only five buttons anyway – they'd want the latest thing to come out.

"Four-year-old kids should be with a responsible adult at all times. They shouldn't need a mobile phone."

Housewife and mother-of-two Joanna Burton, 35, from Boldon, said: "Four-year-olds are too young to have a mobile phone. They shouldn't need it.

"It's completely unnecessary if parents watch their kids properly.

"I wouldn't buy one for my four-year-old, but I watch my kids."

Amy Purvis, 22, a student from Hedworth said: "It's definitely too young, they're just bairns. I just don't think they should have them really.

"They'd probably get broken and it would just be a waste of money, and the kids should be with their parents if they're only four.

"If I had a four-year-old I wouldn't let them wander round the streets by themselves anyway."

Student Devan Carr, 16, from South Shields, said: "It's not a good idea, I don't think a four-year-old really needs a mobile phone.

"They would normally be supervised at four by someone they know and that person should have a phone just in case."

Gary Walker, 41, unemployed, from Newcastle, said: "It's a good idea if it means they'll have contact with their parents. It's a bit like a walkie talkie.

"Four is a bit young though. Parents should be watching their kids anyway, so what would they need a mobile for?

"It's a bit of a lazy way out. They should be keeping an eye on their kids."

Professor Lawrie Challis, who led the Government research on mobile phone safety, said that primary school pupils should not have mobile phones.

He said parents should encourage older children to text rather than make calls, as texting exposes them to lower levels of radiation.

Official Government advice to parents remains that they should avoid giving mobile to under-16s as a precaution.