Bill de Blasio swept from also-ran to mayor-elect on a notion that New York City needed sweeping change, but facing questions about how steady his hand would be as a manager of the massive bureaucracy that is our municipal government. In the trickle of appointments so far, the public advocate has done a lot to answer the questions about his managerial muscle—by bringing in veteran insiders to run the police department and his budget office, and to serve as two of his deputy mayors.

The pattern repeated itself Sunday with the appointment of Gladys Carrion to head the city's Administration for Children's Services, our child welfare agency, which investigates claims of child abuse and neglect, runs the local juvenile justice system and oversees childcare and other services. Carrion has headed ACS's state counterpart, the Office of Children and Family Services, since early 2007.

In that capacity, she oversaw OCFS's response to damning reports by the U.S. Justice Department and a state task force about the conditions in the state's juvenile detention facilities, and instituted reforms—none more important than the closure of several facilities and an effort to house detainees closer to home.

Carrion replaces Ronald Richter, whom Bloomberg appointed in 2011 and many in the child-welfare world hoped and/or expected would stick around. (When I told an interviewer in 2012 that I thought being head of ACS was the one job I would never want because of the enormity of the task of protecting all New York's children, Richter called to tell me that he thought he had the best job in the city.)

So far de Blasio has picked a former NYPD commissioner to be his NYPD commissioner, a Bloomberg commissioner to be one of his deputy mayors and a former Port Authority e.d. to be another, a 20-year veteran of the statehouse to be his budget chief and now a state child welfare official to become a city child welfare official. None of the choices can be faulted on competence. The question that even some de Blasio fans raise is, at what point do you surround yourself with so many insiders that truly substantial change becomes impossible

The obvious rejoinder is that the mayor-elect has to make sure he has skilled people minding the store day to day or else he'll never accomplish his bigger agenda. That was the clear case for Bill Bratton, whose selection as police commissioner bought de Blasio credibility on crime—an issue on which the tabloids were gearing up to hammer him over.

While their jobs are vastly different, ACS and the NYPD reflect similar political risks: High-profile cases of child neglect and abuse, for obvious reasons, will trigger questions about an administration's competence just like crime waves do. Also like the NYPD, ACS is often viewed—particularly in low-income communities of color—as an abusive, outside force. Instead of stopping and frisking you, they take your kids. Richter and others at ACS recognize that reputation and have made moves to alter it.

Child welfare in New York City looks vastly different than it did when Rudy Giuliani—who started ACS in 1996 amid the outrage over Elisa Izquierdo's death—was mayor. In fiscal year 1998, there were on average 41,000 city children in foster care. Last year, there were 13,000. Even the number of abuse/neglect investigations has been trending down.

But for people involved in the system, it is the dominant thing in their lives.

Last week I spoke to a former Bloomberg commissioner, and asked about the insider versus outsider question. How important is experience compared to a fresh set of eyes? The former commissioner said it would have been very difficult to run their agency without having worked there for years—knowing all the players, knowing how policy worked behind the scenes. The hard thing, sometimes, was managing people whom you'd known from before you were the boss, the former commish said.

Carrion will bring some combination of the advantages and disadvantages of deep government experience to her new gig. That's clear. It's also clear that she won't have the transition spotlight much longer: de Blasio has another announcement scheduled for noon Monday, when we'll get another look at how the next mayor plans to play the insider-outsider game.