Parents of tweens, I know what your kids will want to go along with their new clothes and backpacks before school starts up in a few weeks: a cellphone.

Or, if they already have one, a superfast upgrade.

Not too many years ago, kids had to wait until high school to get a cellphone. It was a rite of passage. But now more parents are providing tweens — children ages 8 to 12 — with wireless devices, and in such numbers that marketing experts call this age group the new growth market for cellphone carriers.

A study released earlier this month by the National Consumers League underscores this trend. The study found that nearly six out of 10 parents of tweens said their children have cellphones.

“This survey clearly shows that the use of cellphones is now becoming more entrenched at an earlier and earlier age,” said Graham Hueber, senior researcher at ORC International, which conducted the survey of 802 parents of preteens.

And the marketing efforts probably won’t end with preteens. Need proof? Just stroll down any toy aisle and you’re bound to see the pretend plastic trainers for little tykes.

I understand why parents are buying cellphones for younger children. It’s a sign of the times. Working parents are always on the go, and so are their kids.

As the National Consumers League survey noted, most parents are arming their kids with phones for safety reasons and to be able to track their whereabouts after school and on weekends. That’s why I changed my mind a while back about whether pre-high-school kids needed their own phones.

Certainly, peer pressure plays into buying habits, the survey noted. If tweens see their friends talking on cellphones, they’ll probably be asking for one.

While more families are providing cellphones for preteens, the cost of the service is catching them by surprise.

About a third of households earning under $50,000 — and 23 percent of households overall — said they are paying more for the phones than they had expected.

As a result, these parents said they are exploring ways to control costs, including switching to prepaid plans, putting limits on texting or deactivating the service.

Still, 92 percent of the parents surveyed said they are spending less than $75 a month for the service. Most preteens also are on their parents’ family plan.

Having that first phone is also an opportunity to introduce your child to budgeting. It’s fine to let them pay part of the monthly bill.

If you’re thinking of buying a cellphone for your son or daughter, the National Consumers League suggests going over these questions first:

• Why does your child need a cellphone? For emergency use? Entertainment? To communicate with friends?

• How much do you want to spend for the phone, and for the monthly service?

• What’s the policy on cellphones in school?

• Is your child mature enough to use the phone responsibly and avoid viewing or sending inappropriate content? (Consider filters that block content.)

• Is your preteen in the habit of losing things? Can he handle the responsibility of caring for a phone?

When you start shopping, take your youngster with you to see which phones and features he or she likes, said John Breyault, vice president of public policy, telecommunications and fraud at the National Consumers League.

But, Breyault said, the “last thing you want to do is to buy the first phone you see. Study the market.”

If you’re looking for one-stop shopping research and other product information, check out Consumer Reports, the technology website Cnet.com and the National Consumers League’s report “Parental Controls: Managing Children’s Wireless Usage.”