Spring often arrives late on Cape Cod, like a tourist who has taken a wrong turn somehow. The year that our daughters turned 16, though, spring was right on time.

Patches of daffodils dotted the streets of our small village like broken shards of sun. Amber and Sarah loved these harbingers of spring and often posed for birthday photos surrounded by the splashes of yellow.

 On May 3 of 2000, however, they were two young women on a mission. The joint birthday celebration we always held was over and their friends were hastily sent on their way.

I began to pick up paper plates and discarded wrapping paper, but the girls would have none of it.

“It’s time, Mom,” Amber said impatiently. “You promised you’d take us to get our permits today!”

 Sarah added, “It’s already 3:00 and the DMV closes at 5:00. Can’t we hurry?”

How could I forget? The girls had talked of little else as “Sweet Sixteen” approached. Getting their driver’s permits was the birthday gift they wanted most of all, and they were not about to let me forget it.

Abandoning the double debris that accumulated every year on their special day, I grabbed my purse and a magazine while the girls flung themselves into our minivan, urging me to hurry up. As we drove to the Department of Motor Vehicles in So.Yarmouth, I prayed silently. Dear Lord, help us! Two overconfident teenagers let loose on the roads, skyrocketing automobile insurance rates, one minivan with too many drivers . . . Father, help me find the humor in this situation!

Amber and Sarah were not the only teenagers in our home eager for wheels and independence. Their older brother Adam and younger brothers Matt and Jordan were constantly on the go as well. With five teenagers filling our modest raised-ranch home, we needed humor to survive, and the kids could be counted on to provide it.

Adam, Amber, and Jordan were born to us, but Sarah and Matt had come to us three years earlier when a series of events left them without a custodial parent. Sarah and our biological daughter Amber became fast friends in fourth grade when they discovered their mutual birthday, and every year since the girls had celebrated together. The close friends had now become sisters—foster sisters.

And I was their mom. Qualifying adjectives like “foster,” “adoptive,” or “biological” are irrelevant when you’re raising children. For the years that my husband and I were privileged to have Sarah and Matt, I was their mom. Period.

The teenage years are a challenge whether you have one teen or five at a time, as we did. Yet never once during their adolescence did our biological kids even hint that we shouldn’t have opened our home to two more children. They accepted their new siblings into our family as God accepts us – without qualification.

The girls’ relationship was a complex one, though. Other than the circumstances in which they had been raised, Amber and Sarah had so much in common:  the same birthdate, school friends, and church youth group. One was first chair clarinet in the school band – the other second chair. Both were excellent students.

As the girls moved into their high school years, however,  differences emerged. One liked jazz; the other rock. One wanted the best grades; the other the most friends. Once close friends and allies, the girls now seemed at times more like intimate enemies.

And also competitive ones. Neither wanted to come in “second” in anything, and that included getting her driver’s license. When we reached the DMV the afternoon of their sixteenth birthday, I settled into an uncomfortable plastic chair with my magazine while I watched the girls negotiate the lines of applicants together.

When they reached the head of the line, I noticed that the usually efficient clerk seemed to be taking her time studying their paperwork. She glanced at the girls, looking from one to the other, and then returned her gaze to their applications. What could be taking so long? I wondered. She’s approved other permits in a fraction of the time she’s kept Amber and Sarah waiting. I closed my magazine and walked up to join them.

I didn’t have to wait long. “Are you their mother?” the clerk said with a frown.

 “I sure am,” I answered.

 What had we done wrong? Had I failed to make sure the girls brought the right documents?

 “What seems to be the problem? Is everything OK?”

“Oh, everything’s in order,” the clerk responded. Now it was her turn to look embarrassed. “It’s just that your daughters have the same address, same phone number, same parents listed. It’s all right here. And the same birth date: May 3, 1984.”

Sarah turned to me anxiously while Amber simply looked exasperated.

“Yes?” I responded cautiously.

“Well, I know it’s really none of my business but . . . they have different last names!”

 I stared at her for a moment and then grinned. New Englanders are not known for inquiring into others’ personal business, but it was obvious what she was thinking: Twin girls with different fathers? Just how did she manage that?

Eager to get on with it, Amber set the matter straight. “One of us is a foster,” she explained.

 The clerk examined brown-eyed, brunette Amber and then fair-haired Sarah. She stared again at me. “Oh-h-h,” the clerk said, nodding sympathetically at Amber. “Aren’t you lucky they took you in.”

But it was Sarah—born not of my body but in my heart—who had the last word.

“We’re both lucky,” she retorted as their permits were approved.

We turned to leave, and I lagged a few steps behind as the girls hurried out to the van, sparring good-naturedly over which one should have the privilege of getting behind the wheel first. Tears suddenly formed in my eyes, surprising me. No, I’m the lucky one, I thought.

I had not given Amber a sister, but God had. Sarah needed a home, and God had given her one.

Two unique young women born on the same day of the same month of the same year to different families, now living as sisters in the same home.

Remembering the clerk’s confusion about their last names, I smiled.  I should have told her the most important thing Amber and Sarah had in common.

 The same Father.