The show was in the 90's. If I remember correctly, the alien/babysitter is either an imposter posing as an aunt/mother of one of the main characters. The main characters are children, who discover the person is an alien, because she pricks her finger on a rose and it bleeds a different color. (I THINK) They also discover that water harms the alien and use that do destroy her. (In a pool, if i remember correctly) ANY IDEAS, GUYS??
"I'm an addict; I turn everything up to an eleven." - House, M.D.