1. Offer to come over on a Saturday night. We're not always up for a night out—when, we admit, we're tallying up how much the babysitter is costing us—but we do want company and fun. So if you don't have big plans, hop over for some wine and a movie after our kids are in bed.

2. When you're with your single-mom friend and child, take pictures of them together. We know many mothers don't get in the picture, but this is especially true for single moms.

3. Send her a birthday card or a small holiday gift on behalf of her child. Trust us, your friend's heart will melt with gratitude.

4. People often say, "If you ever need a babysitter..." Here's the thing: We're probably never going to call you. We feel awkward and don't want to impose. Instead, maybe meet us out for a quick coffee with our little one and then offer to take our child for an hour. We can grocery shop, get a manicure or run a quick errand—gals like us can move mountains in 60 minutes.

5. If her family lives far away, invite her over to celebrate Mother's Day with yours. We often have to create our own special day. Same goes for New Year's or Valentine's Day. An invitation to your party—or a girls' weekend—means the world. Even if we can't swing it, we love knowing we're still in the mix.

6. We take a deep breath and walk into most events alone. Attend parent-teacher conferences with your single-mom friend. Sit in the stands at a T-ball game. Go to a dance recital or swim class. Moral support is everything.

7. Loan out your in-laws. The next time the grandparents visit, invite your single-mom friend and her child. We often have half the amount of grandparents but want our kids to experience more of the gifts only that generation can bring: the story read slowly, undivided attention, an extra cookie snuck past mom. Every village, no matter how small, needs their elders.

8. Some days, 10 p.m. is like the finish line to a marathon we didn't train for...and at 3 a.m. the worry wheels start turning again, with no pillow talk. Send her a quick good-night text to remind her that she's not alone.

9. Next time you see her, tell her she's doing a good job. Just because.

Erin Sermeus, 40, is a single mom to her daughter, Astor, and her Yorkie, Cowboy. She is vice president of booking and talent relations at Harpo Studios and lives in downtown Chicago.