I think it's perfectly reasonable to say that you need to find a full time position, that they have been fine employers but you need a different work/life balance.

If you give them a month's notice I think that's extremely fair and it doesn't matter that it's in the middle of the school year.

Nannies almost never share the real reason why they're leaving. Seems better to gloss over any issues.

If you feel the need to give a reason I would just say that you are now looking for a full time job and leave it at that. Probably no need to tell them that the kids fighting causes you anxiety or anything like that.

I don't think you need to get into why you are leaving but I do think it would be fair for you to make sure that they know that it isn't anything wrong that they have done.

I'm going to put in a notice soon. I'm a PT nanny to 2 and I plan on giving at least a one month's notice. I don't have any specific complaints about the family or the kids. They family has been pretty good to me, and aside from some minor communication issues it has been okay. But I know the job isn't for me anymore, and at the end of the day I feel devoid of any life. The nature of the job forces me to have to work an additional job in order to make enough money to pay all my bills, and working 2 jobs is starting to affect my performance with the kids. I just don't like doing this anymore, I always feel on edge like I did something wrong, or something might go wrong. The kids fight frequently and my stomach is always in knots, bracing for the next blowout fight that I have to break up.

It's not them, it's me, I realize that. This job as exacerbated an anxiety problem that I didn't realize I had. When putting in my notice, should I even bother mentioning why I'm leaving?

Also, is it bad to quit in the middle of the school year? Initially, I was going to wait until June to give notice, but I don't think I can wait that long.