My kids are so into it this year! I don't think they really get it though... they just say something untrue and then immediately blurt out, APRIL FOOL'S! Example:

My daughter: Daddy, I pooped in my pants.
Me: *Ugh, just kill me now* <-- thought bubble
Daughter: APRIL FOOL'S!!

Actually I take it back, that was a pretty good April Fool's. In years past, they'd do unspoken April Fool's. Example:

Son: *I'm going to pretend I'm going down for a nap.*
Me: *Oh thank goodness, I need this break so much!*
Son: *Haha, got you, I'm not even tired - APRIL FOOL'S!!*

Are your kids into April Fool's?