It’s been almost eight months now, and my daughter and I still don’t have our song. Her older brother, Sam, and I have an album’s worth. I crooned a rotating playlist of off-pitch lullabies — “American Girl,” “Sweet Baby James,” “Me and Bobby McGee” — to him every night for the first two years of his life. But when Eve needs extra help drifting off, I can just hand her off to her dad. This is amazing. And it worries me.

I was a single mother by choice when Sam was born three years ago. In the wake of a bitter divorce, my doctor informed me that my ovulation day was bouncing around the calendar with all the predictability of a roulette ball. This would make conceiving a baby difficult, he said, and I was already 34. He advised me not to wait if I really wanted a child. I did, very much so. Framed as a choice between single parenthood and possibly no parenthood at all, the decision made itself: I chose a sperm donor, took a few cycles’ worth of ovulation-stabilizing hormones, and within a few months, Sam was on the way.

So, when he arrived, there was no partner to tap in when I needed a break. And while that was cry-in-the-shower hard at times, I think it also granted Sam and me an airtight bond. A few years later, I find myself happily married and sharing both the drudgeries and joys of parenting — and afraid that my relationship with Eve will suffer for it.

On those early, bleary-eyed nights with Sam, rocking and shushing and toggling his white-noise stuffed panda between “Ocean Waves” and “Babbling Brook,” I felt it in my gut: This child was my responsibility. I was judge and jury to all the decisions that would shape his life, from sleep training methods to his first food to my vision for the kind of man he would be. But if the work ahead of me was breathtaking, so was my love for him.

Let me be clear: I had a flexible job, the savings to take an unpaid maternity leave and, most of all, extraordinarily supportive parents who embraced a new Grandpa-and-Granny nanny role. Even with all that privilege, single parenting is exhausting and dispiriting on its worst days. I weathered the full force of my son’s diaper blowouts, tantrums and boundary-pushing. But the flip side is a bond between us that buzzes with intensity, like any romance, drawing power from its exclusivity.

I was Sam’s uncontested favorite for comfort when he bonked his head, for playing Legos, for baths and for bedtime stories. Rather than a teddy bear, he chose my ponytail for his comfort object.

And all this relationship building was going on during the developmentally critical first year of Sam’s life. “Forming attachments is a biological mandate that is deeply baked into early human development,” said Dr. Ross Thompson, distinguished professor in the Department of Psychology at University of California, Davis. He noted that developing a secure relationship with at least one adult could be an evolutionary tactic for survival: In the first months of life, infants need an emotionally invested caregiver to feed, clothe and protect them from roaming predators.

And studies with rats have shown that the quality of care a pup gets during early development can change the way the brain grows — findings that have been echoed in a human study of the brains of victims of childhood abuse.

Dr. Susan Golombok, director of the Centre for Family Research at the University of Cambridge and author of “We Are Family: The Modern Transformation of Parents and Children,” has examined the quality of single parent-child relationships in particular. In two small studies comparing single mothers with couples, she said, “there were closer, warmer relationships between the mother and the child” among the fatherless families. There was also more conflict between the mother and child. Generally, her research shows that in single-mom families, “It seemed to be that the relationships were a bit more intense. There’s a lot more of everything going on,” she said.

I grew used to the idea that Sam and I would face the world as a happy little family of two. But when he was 18 months old — to everyone’s surprise, including my own — I fell in love with a close friend. Norman opened his heart to Sam from the start, I got pregnant, we got married and he adopted Sam. One month after that, Eve arrived.

I imagine that life gets tougher and more complicated when other couples welcome a second child. But in my house, the extra chaos of a new little family member was canceled out by the enormous help of a second adult with an equal stake in the game.

This time around, somebody else was just as thrilled as I was with Eve’s first smile. Somebody else was excited to spend an hour talking about her pooping habits. And watching Norman pour his love all over both of our children brought tears to my eyes. Instead of just one primary adult revolving around them, Sam and Eve now have double the adoration.

Still, I’m not the only one Eve turns to when she’s crabby or scared. Her dad can get her down for a nap faster than I can. And part of me wonders if she giggles more when Norman tickles her. Could the abundance of love in our family somehow dilute the relationship I’m building with her?

There’s not much research looking into our particular situation. But the developmental psychologists I spoke with reassured me. “What really matters more than anything is the quality of the relationships in the family,” said Dr. Golombok. Besides, her work suggests that, as intense as the bonds between single moms and their kids can be, the effect fades after the first few years.

Natasha Cabrera, director of the Family Involvement Laboratory at the University of Maryland, also studies the effects of single versus partnered parenting on kids. She said, “It all boils down to the relationship — it’s so specific to that child. This is your daughter, who in many ways is so different from your son.” A new set of variables are in play now, including Eve’s temperament (mellow where Sam is exuberant) and the couple years of experience I’ve racked up.

I never feared that my two kids would compete for some finite amount of love in the house. So why would it be any different with Eve’s bond to two parents? For all the importance of the early parent-child relationship, “attachment isn’t a zero-sum game,” said Dr. Thompson, drawing on decades of research on attachment theory. “If you’re securely attached to one adult, it doesn’t leave less security for you to invest in another.” What’s important is that a child forms a healthy connection with someone, which lays the groundwork for more attachments to come.

Honestly, part of me wants it to be true that single parents have stronger bonds with their children. Solo caregivers have it so tough, it seems only fair they at least get this small mercy. But the other part can’t accept that my relationship with my daughter is destined for second-class status.

So maybe it’s up to Eve and me to forge a bond on our own terms, just as Sam and I did and still do. Maybe it’s ridiculous to look at my husband — who does diapers and dishes and takes both kids on their own special daddy-kid dates — and feel any kind of jealousy and anxiety. Plenty of other parenting worries await us, I’m sure. Too much love doesn’t have to be one of them.


Elisabeth Kwak-Hefferan is a freelance writer and editor based in Missoula, Mont.