NEW YORK — Ronald McDonald is having a midlife crisis.

His floppy shoes, painted-on smile and flaming-red hair may be a harder sell to today’s kids who are trading in their dolls and trucks for manicures and mobile game apps at ever younger ages. He also seems out of step with McDonald’s Corp.’s new efforts to appeal to adults. The 48-year-old spokesclown has fallen flat in new ads this year, according to Ace Metrix, a group that tracks TV advertising.

And the government is getting strict on marketing unhealthy food to children. That has both marginalized Ronald as more of a mascot than a product pitchman and landed him in the middle of the bigger debate about food makers’ responsibilities in stemming the rise in childhood obesity.

McDonald’s says it is proud of the food it offers and that Ronald teaches children to be active. Critics say it’s time to hang up the yellow jumper.

A group called Corporate Accountability International plans to ask Ronald to retire at the company’s annual meeting on Thursday. They say Ronald encourages kids to eat junk food, contributing to a rise in childhood obesity and related diseases such as diabetes.

The group, which campaigned against the Joe Camel cigarette mascot in the ’90s and complained about Ronald as a role model at McDonald’s annual meeting last year, has stepped up its campaign. The group took out full-page ads today in several major metropolitan newspapers to call for his head. The ads, signed by more than 550 health groups and professionals, carry the headline, “Doctors’ Orders: Stop Marketing Junk Food To Kids.”

What follows is an open letter to McDonald’s CEO Jim Skinner, that says in part, “We ask that you heed our concern and retire your marketing promotions for food high in salt, fat, sugar, and calories to children, whatever form they take — from Ronald McDonald to toy giveaways.”

McDonald’s defended Ronald against the group’s attack at last year’s annual meeting and is adamant that it has never considered downplaying its smiling mascot. “It’s totally unfounded,” said Marlena Peleo-Lazar, the company’s chief creative officer.

New commercials show him as an active, athletic clown who encourages kids to visit McDonald’s, Happymeal.com website.