When did you not speak up when you should have?

I was sitting for a toddler at his brother birthday party. There was a buffet of snacks for the kids, so I went and got a plate of a few things for the toddler to munch on before dinner in another hour. I sat down with him, he took a couple bites, and then went to run behind his brother on the dance floor area. I popped one more chicken bite in my mouth, was going to take one more sip of my water, and then go follow/be with him. The dad comes over RIGHT at that moment as I'm about to stand and says "where's N?" I replied he ran after his brother, and I'm heading over now. And he goes Ok, "just watch and be with him." I wanted so MUCH to say he JUST left not even a minute ago , but froze. I hate ANY confrontation esp. with a boss. He thought because I was sitting and sipping my water that I was just doing that the whole time, or was GOING to be..it was the furthest thing from the truth. I watch children in my care very well and am rarely ever not with or near them. I never heard from them again because I didn't speak up.😕

All the time, I’m very soft spoken naturally
I’m getting better about standing up for what I believe in now
But I let a lot of things go, especially in high school

My issue is not being able to be quiet. I have this overwhelming feeling in me when I see something I think needs addressing.