How do you all say no in a nice manner when rejecting your spouse request for sex?

Normally, I will just let him know the truth I.e. I'm too tired or I just don't have the mood for it. Most of the times he understands as I have to care for both my kids alone. Although it may hurt them a little bit but truth is always better. Or you can talk to him about it during daytime on why you are not into it.