Anyamal Tantei Kiruminzoo might work, if you can find it (I have no idea who holds the streaming rights right now, if anyone). Comedy-adventure about kids who find a device that lets them turn into animals. I don’t remember it having anything too heavy in it, although admittedly it’s been a few years.

In a couple of years, Detective Conan / Case Closed might be good (and will keep you busy for a very long time), but six is probably a bit too young.