The best light is always the hour after sunrise and the hour before sunset.  If kids are involved in your portrait session, I would suggest we meet in the early morning when they are feeling sparky and we adults are not.  If your session cannot occur in these hours, don’t worry, we will work together to do the best we can.  There are always solutions, like assistants holding giant umbrellas and utilizing shade under trees, of which there are plenty in the Tahoe area.