How do I deal with this?... [View all]

Have my grand-kids for the weekend. They are both girls... 9 and 12 yrs old and they are great girls, but...they are obsessed with slime.
Have any of you dealt with the great slime menace?

I am an artist a painter and sculptor and I have to say as broad minded as I am bout crafts... I just don't get this.

They are constantly playing with it and posting vines of it and they view the prefect slime as some sort of achievement.
Can anyone talk me down?