Smartmom and Diaper Diva may be twins, but Smartmom has always felt like the elderstatesmom when it came to raising kids.

For Buddha’s sake, Teen Spirit is 13 years older than Ducky. That alone gives Smartmom the right to act like a big know-it-all, doesn’t it?

For many years, Smartmom was the Been-There-Done-That mom around her sister and she always thought she knew best what Diaper Diva should do when it came to Ducky.

It was probably really annoying. Actually, it was really obnoxious. But Diaper Diva was pretty nice about it. That’s probably because when Ducky was little, Diaper Diva was a typical new mom: a little nervous, a little jittery, a little bit, let’s call it what it is, ignorant when it came to the basics.

And boy did Smartmom love it when her sister asked for her advice. It made Smartmom feel like such a pro to give tips about teething, temperatures and the terrible twos.

Smartmom loved it when Diaper Diva followed her instructions word for word, like the time she bought the exact same Braun ear thermometer at Neergard or invested in the exact same kind of Maclaren stroller.

And then there were the times when Diaper Diva didn’t listen to what Smartmom had to say — something she lived to regret.

How about the time when Smartmom told Diaper Diva that she should get all the birthday party balloons in the same color so that the kids don’t fight.

“Read my lips,” Smartmom said. “Twelve purple balloons.”

But Diaper Diva didn’t listen, and at Ducky’s birthday party a gaggle of girls fought over two pink balloons.

There were tears and tantrums — and more than a few “I told you so’s.”

Then there was the time that Smartmom told Diaper Diva that it was a definite no-no to go backstage with Ducky before the Dance Studio’s recital at Brooklyn College.

“They don’t want parents back there, and she’ll probably get very clingy,” she warned.

Diaper Diva didn’t listen to Smartmom that time either. And when the rest of Ducky’s class was performing pirouettes, Ducky stayed stubbornly in Diaper Diva’s arms far away from the stage.

Well, that was then and this is now. Ducky is 5, and Diaper Diva is an experienced mom. Truth is, she doesn’t really need Smartmom’s advice anymore. And sometimes that makes Smartmom feel sad.

In fact, it doesn’t just make Smartmom feel sad. It makes her feel old and obsolete. It makes her feel invisible and without a purpose. She doesn’t know who she is when she isn’t being elderstatesmom.

Change is tough.

Diaper Diva doesn’t need Smartmom’s advice when Ducky has a fever. She knows all about Children’s Motrin and cold baths.

Diaper Diva doesn’t need advice about Ducky’s birthday parties. She knows the best hula-hoopers, children’s folk singers and party clowns.

Diaper Diva doesn’t need Smartmom’s advice about summer camps. She’s familiar with Park Explorers and Kim’s Kids and has actually researched, like, 10 other camps in the area.

Diaper Diva doesn’t need Smartmom’s advice about disciplining Ducky. Diaper Diva is actually an ace when it comes to setting limits and telling Ducky that she can’t buy junk eggs at Pino’s, those stupid little toys in egg-shaped canisters that they sell in those evil gum ball machines.

Smartmom can’t give Diaper Diva advice about bedtime either because, well, her kids were (and still are) night owls. But Ducky has always been a great sleeper, and Diaper Diva has always been firm about putting her to sleep, after three books, at 8 pm.

And about that three books thing, Smartmom lost that battle early on. She was never able to limit the number of books she read at bedtime. Well, she tried. But Teen Spirit, and then OSFO, always pushed the envelope.

Smartmom can’t even give Diaper Diva advice about PS 321, the beloved elementary school where she sent her children. For one thing, Smartmom doesn’t know all the new teachers. And Smartmom is way behind the eight-ball when it comes to all the newfangled traditions like 100s Day, the 100th day of school when the kindergartners are required to create an artwork using 100 of something.

Smartmom isn’t Expertmom anymore. So it’s lucky Smartmom isn’t having any more kids because she’d never hear the end of it from Know-it-all, er, Diaper Diva. Truth be told, she’s the smart mom now.