Have a client that wants to record audio on some indoor cameras located in kitchen/ family room and possibly baby's room.
Has anyone used mics on indoor cams? Not even sure if it's legal.

Yup. Some work better than others.
Check local laws but in most residential areas I've seen it's allowed.
I have several in my house but as I said, it's OK for loud noises but not for making out quiet conversations.

It's mainly for the kids and the caregivers, to keep them in check.

"Nanny cam" video is legal in all 50 states. Most if not all have rules that dont permit recording in "private areas" like bathrooms and bedrooms.

Audio recording without consent is legal in 2/3 of the states. The other 1/3 requires that you notify/receive consent. The best way to do this IMO is in writing in an employee agreement of some sort.

If it were me...i would just do it anyway. The primary goal is to keep the kids safe. If you ever have an issue just strip the audio from the video and present that as evidence.

Nest Cam?  Ring Cam?

I set up one by a cash register in a feed store. Its works and works well. Hears all the conversation. It's from when Luma first came out.

My company has one. I think it's legal but people don't usually use it except for the baby's room. No need for other rooms.

Hikvision

Recording audio, even in your own home, is under more control than video. Check local laws. And when they say it’s ok, still post the property

WHAT?? In your own home? There should be ZERO laws about what I want to do with audio in my own home. Way over reach. Fugg that. Come and get me.

The laws aren’t for you; it’s for your guests...and your pissed off teenager that decides to sue you ;-)

In most states you can secretly video tape even private areas in your own home as long as the people recorded aren’t minors. But adding audio to it changes everything.

And audio is actually more incriminating than video.

But audio is easily defeated, while video can only be defeated by actually blocking the light.

Audio is defeated by background noise in the room, or competing voices, or natural room echo, and by distance from the mic, which exaggerates all these problems.

You want to have the mic a s close to the person speaking as possible. You want the room quiet, only one person speaking at a time, and sound deadening material in the room. That last item is easily carpet and a couch.

That’s why they created such mics to overcome that problem, Ernie.

[Link: audixusa.com]

Id still recommend running any mics into a dsp of sorts and then using an output of that dsp to the camera.