Flint the Time Detective
Absolute Anime; ANN; IMDb; TV.com; Wikipedia

I never watched too much of this, and it hasn't been on for quite awhile. It really wasn't great, but I guess it could be kinda funny. There was this bureau of time police, and they recruited this little kid from the stone age named Flint. And his father was a big stone hammer for some reason, which Flint would hit enemies with. There were some other kids, too, from like the present. And there were little critters which I think were called TimeShifters, which the bureau wanted to get ahold of. But there were some evil folks who also wanted to get them. The Shifters were all in different eras, helping out famous people from history, and the time detectives would go back in time and fight the villains for control of the Shifters, then erase the historic people's memories of all this before they returned to the present.