The new curfew law that Mayor Nutter promised this summer after youths were arrested in a series of random beatings in Center City is slated to be introduced in Council on Thursday.

The bill, which Councilwoman Blondell Reynolds Brown plans to introduce on Nutter's behalf, would make several structural changes to the current law and comes after weeks of discussions on the most effective way to employ curfews.

Nutter spokesman Mark McDonald said the goal was a law with a "more developmentally appropriate" doling of rights to minors.

Primarily, it would lower the hours when unaccompanied minors can be on the streets, and would set distinct curfews for three age groups - 13 and younger; 14 and 15; and 16 and 17.

The current law sets curfews only for two age groups - 12 and younger, and those 13 to 17, who now are permitted out until midnight on weekends.

The new category for 14- and 15-year-olds creates "a middle ground that speaks to the developmental growth that occurs in that age group," McDonald said.

"They're not lumped in with the older group, nor are they shunted down with the 12-year-olds," he said.

The current law also sets different curfews for during the week and the weekend. The new curfew would apply all week.

"That is more realistic to what youth behavior is all about," McDonald said. "Meaning, young people are out on any given day."

The new law also would be structured around the school year. When school is in session, children 13 and younger would have to be off the streets by 8 p.m.; the 14- and 15-year olds by 9 p.m.; and the 16- and 17-year-olds by 10 p.m.

In the summer, each age group would be given an extra hour.

"For all three age groups, the thrust of this is earlier times," McDonald said. "There's no more midnights for these children."

In August, Nutter unilaterally dropped the curfew for all minors to 9 p.m. on the weekends in Center City and University City, and those neighborhoods were flooded with police after a series of "flash mob" attacks.

The new curfew would apply equally across the city, with no special times for certain areas.

The bill also allows for parents to be fined if their children are caught violating curfew, and parents could be held liable for any other criminal acts committed by their offspring.

In conjunction with the lowered curfews this summer, Nutter ordered 20 of the city's largest recreation centers to expand their weekend hours. Eight of those rec centers continued those late hours after school started.

Nutter has talked about a "holistic approach" to the problems facing teenagers in the city, and McDonald said the new curfew law was "the first part of a broader discussion of youth violence."

He promised that proactive measures would be "ramped up" in the coming weeks.

Contact staff writer Troy Graham at 215-854-2730 or tgraham@phillynews.com.