There are lots of firsts in our children’s lives: First steps, first days of school, first kisses, and first drives alone.

The first time your child loses her tooth is not under your control. It’s going to happen when the tooth is ready, regardless of whether your child is 4 or 7. But there are several firsts for which parents control the timing. When can your children first stay at home by themselves? When can they first take public transportation to school by themselves?

While statistically the city is much safer than it used to be, almost all the parents I spoke to felt that the “world is just a different place.”

“So what if fewer people are murdered in the city each year?” a mother who was raised in the city and now has three children said. “It might not be rational, but I just don’t want my kids on the subways when there are terrorist threats every few weeks.”

It seems that worst-case scenarios are a determining factor for parents when deciding at what age their children are ready to take on the responsibility of staying home by themselves and going to and from school alone.

“Luck plays such a scary role,” a mother of two middle schoolers said. “If everything goes smoothly, well, then of course your child is ready to be by himself at home, or walking across 86th Street. But what if there’s an accident or something else that you can’t really predict? It might not matter if your kid is 11 versus 14. But maybe it might.”

Many parents said that the route a child takes to school and whether there was a friend nearby to make the step at the same time determined the age at which they felt ready.

“The big cross streets are a nightmare. Having my 11-year-old son take the crosstown bus with a friend makes it more manageable. It seems less likely that a crazy cab driver will not see two kids, as opposed to one,” a mother of three said.

All the parents who have been through these firsts were quick to point out that sometimes there were variations among siblings.

“My first son is so responsible, he was ready to walk to school by himself in fourth grade,” a mother of three said. “So of course my daughter, who is two years younger, thought she was going to walk by herself in fourth grade, too. But the truth is that she’s not nearly as responsible. She spaces out, and I basically had to tell her that she wasn’t ready to go on her own. Only a year later, at the end of fifth grade, did I feel comfortable letting her go. She was mad, and I can understand why. But these are safety issues.”

Some parents were reluctant to discuss the age at which they allowed their children to stay home alone.

“You’d better not put my name in,” began one mother of two boys, “but I left my 9-year-old alone the other day – but just for an hour. You’d better not turn me in,” she said, giggling nervously. (She needn’t worry: According to New York State’s Office of Children and Family Services, there is no specific age at which children are legally allowed to stay home alone.)

One mother I spoke to felt that her 11-year-old daughter was capable of staying home by herself and watching her 5-year-old brother.

“We were eight blocks away at a school meeting. The doorman knew we were out. Our cell phones were on. I must say that I was a bit uneasy, but it turned out to be fine, and we’ve done it again since,” she said. “They both love the time together and my daughter feels very grown up.”

Many parents told me that 13 was a magic number.

“I leave my 13-year-old in charge of his two younger siblings, but I think part of the reason I am able to do this is that they all get along. My eldest takes particularly wonderful care of my youngest,” one mother said.

It is clear that these decisions are case-specific. “My 13-year-old son is less responsible than my 8-year-old daughter,” one mother said. “Needless to say, we don’t leave either of them on their own. Soon, I hope. But I’m not holding my breath.”

sarasberman@aol.com