On the strategy of:

don't call her out on it, if she is, you will only get trickle truth at best, and plain lies at worst. Then she will hide things better (assuming they are there). Now I go with the assumption that a guys instinct on these things is there for a reason, so if you have to bullshit yourself into thinking it's nothing, there's probably something there.

If you really want this piece of mind so you can make a decision, I would suggest think through your limit. What would it take for you to throw in the towel. emotional affair? Making out with a dude? blowjob? fucking him? at the expense of parent duties? Deception of any kind?

If you aren't willing to divorce her over it, child or not, than you don't care, and need to get over it. this is about owning your shit in that regard. there is no right answer here.

If you want to deal with it.

I really should save more of these links I refer to, way back in here, was a reference to the rollo article about girls nights out, or maybe some of the reading on the sidebar.

the one line I remember was 'that isn't appropriate behavior for a married woman' But there was a lot more about it than I could give here. The gist was to set a boundary, and be prepared to enforce it. Do you really care about cheating, or is it more important right now to avoid the possibility of deception? This is the exact kind of exestential question my post on mental models addresses. You need to know what the underlying emotion and reason you are in the state you're in, and not the bullshit you think it is. No matter how bad it sounds, keep asking yourself why something bothers you until you get into the banality, that's pretty much the REAL why.

The one simple thing you can do, tell her to give you her phone, and then stfu and watch her. That will probably tell you everything you need to know. This is the kind of thing you have to have a strong frame to pull off, because the more guilty she is, the more shit, shame and pressure you will get to avoid it. If you don't have frame, you can always grab it when she's in the shower and scan the obvious.

If you want to be a spy

I would suggest having the line I talked about in the first para in your head before you even start down the rabbit hole. This shit tends to involve a lot of ego protection and hamstering if you aren't prepared. Be aware, this beta shit is a necessary evil if you do it, and is a huge loss of frame, abundance. But you are your own judge.

Can't find it at the moment, but there is the adultery busting post linked here, with all the spyware. I don't like reading it, it's like taking an alex jones podcast as gospel, gets me paranoid. I'm sure someone has it and can link. Keep in mind that with smartphones, if she's clever enough, theres no way you will find out, short of GPS tracking her car etc. Would be a good time considering what state your relationship is in if this is what you have to do for peace of mind. the suggestion was for GPS trackers, one in the car, one in the purse, voice activated recorders, dr. fone sofrware, the works. Any james bond fantasy here. If/when she catches one of them, be prepared, since at this point, I would worry if ones frame could handle it. I would suggest a time limit to this stuff, just in perpetuity seems weird to me, if you're unsure for that long, might just be easier to say fuck it.

Or you can do what /u/ultimatecad did, give her enough rope to hang herself. set up a gps tracker in her car, ask her innocently some questions you know the answers to, see if the answers jive. You won't know what happened, but you'll know she was lying. For him, it was enough for him to take action.

For me, simple social media and phone perusal when the opportunity presented itself. Saw what I needed to see, didn't say anything further, or confront her. Though for me, she came clean, with no chance of me finding out otherwise, which fucked me up for a while. Kind of went against everything I've come to know about cheating women, and it took me a while to get over the trickle truth fear.

At the end of the day, I have a trust, but verify attitude. There's been many emotional cry fests early on to my MAP, a main event, and very clear demonstrations that I am prepared to move on if I get the impression I'm being taken advantage of.

I don't think I would have gotten there with a GPS tracker.