Quoting LittleBear's mama:" Kids aren't stupid, they can see if you are unhappy, they can sense it. Better to be honest but guarded ... [snip!] ... guarded honesty. Admit you are unhappy but tell them in a way they will understand, make it for their level of understanding."
I agree, being honest is a good thing, although sometimes we do need to be guarded in just how honest we are. Kids can misunderstand some of the simplest things. For example, my 4 year old went to his grandma's house to stay for the weekend and he was putting off leaving saying he wanted to come back and play some of his video games before staying the night with her. She explained that he could come to spend the night but she wouldn't be bringing him back home to play video games that night, he completely misunderstood and we found out that sunday that he had willingly agreed to say goodbye to mommy forever and just live with grandma, lol. My heart was a little broken that he had consented to never come home again, but he was extremely happy to see me. He's 4, so his concepts of time are still a bit skewed.