NOT long ago, many parents wondered at what age they should give their child full access to the car keys. Nowadays, parents face a trickier question: At what age should a child own a smartphone?

The smartphone, after all, is the key to unfettered access to the internet and the many benefits and dangers that come with it. But unlike driving a car, which is legal in some states starting at the age of 16, there is no legal guideline for a parent to determine when a child may be ready for a smartphone.

The topic is being increasingly debated as children get smartphones at an ever younger age. On average, children are getting their first smartphones around age 10, according to the research firm Influence Central, down from age 12 in 2012. For some children, smartphone ownership starts even sooner — including second graders as young as 7, according to internet safety experts.

“I think that age is going to trend even younger, because parents are getting tired of handing their smartphones to their kids,” said Stacy DeBroff, chief executive of Influence Central.