We've all seen it happen or done it ourselves. Your child is playing with a new kid, and the new kid does something not so nice. Do you speak up? Do you look around and wait for someone else to speak up? Learn why it's vital that you talk — and when it's wise for you to walk!

My husband recently watched as an older girl pushed our 3-year-old son off a chair. The mom witnessed the interaction and treated it lightly as our son burst into tears. Unsure what to do, my husband consoled our son and kept quiet.

Here are five reasons to speak up — and some equally helpful "when to zip it" guidelines.

1. Children need to learn to be kind even when Mom and Dad aren't watching.

Linda Buxa has three children, ages 8, 10 and 12 years old. Buxa says if a child misbehaves or uses hurtful language around her, she will speak up. "Trust me, I've been the mom who is not paying attention on the playground. Sometimes you're just so desperate to talk to other parents. I also couldn't keep my eyes on all three kiddos all the time. It's an impossible task."

2. Kids must learn to respond to feedback from strangers.

Kids will go to school and be expected to listen to and follow directions from teachers and other adults.

"They say it takes a village to raise a child. And yet, many parents cringe or get downright angry when another parent intervenes on a behavior issue at the park," says Katie Hurley, LCSW, allParenting writer and author of Practical Parenting. "Kids need to learn to cope with input (even if it feels critical) from other adults. They will go to school and be expected to listen to and follow directions from teachers and other adults."

3. Little ones need constant reminders. Speaking up shouldn't be a loud, angry ordeal.

"We all need to look out for the safety of all kids when we are in public play spaces," says Hurley, who has a 6-year-old daughter and a 4-year-old son. "Sometimes that means redirecting a child that isn't ours. It really shouldn't be seen as a negative. It's an extra set of hands providing a calm and gentle reminder when something isn't right."

4. I want to know that my child will learn from others when I'm not there.

Kids need to be told: 'That's not OK. That's unsafe. Your language is mean.'

"Adults are the ones who are supposed to train our kids," Buxa says. "Kids need to be told: 'That's not OK. That's unsafe. Your language is mean.' Now, I'm not encouraging yelling at the kids, so I'd do this in a firm and gentle voice."

5. Speaking up teaches our own kids to stand up for themselves and address wrongs.

"Speaking up in front of our kids has the added benefit of teaching assertiveness skills," Hurley says. "When we simply ignore the behavior and walk away, we teach our kids to stand down in the face of negativity. When we stand firm and confront the behavior, we teach them to assert themselves when something isn't right."

When to shut your trap

  • The child's parent is already responding.

"It drives me bananas when, once I've initiated discipline, another adult thinks they need to verbally pile on," Buxa shares.

  • The child is just "a little out of control."

"I bite my tongue if I just see a kid who might be a little out of control," Buxa admits. "Let's cut each other some parental slack. It could just be a really bad day. We all need a little grace."

  • You've experienced the just-walk-away trifecta

Popular blog Mostly True Stuff advises: "Don't 'shh' other people's kids if: 

  1. The parent is right there and is trying to calm the child.
  2. The child is not being disruptive, but is merely humming to himself a little.
  3. The parent tells you the child has autism and is doing the best he can.

MTS continues: "You know what? Screw it. Don't 'shh' other people's kids. Ever. Mind your own damn business."

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Read more about children's behavior

Love your kids: How discipline shows you care
Why I chose to publicly shame my child as punishment
Would you turn your kid in for bad behavior?