Both! As they hatch they will hang onto the slate with a mucus slime that is secreated from the babys head, as they fall off the mother will pick them up in her mouth and spit them back onto the slate. If there is no mom/dad to do this then the babys just lie on the bottom of the tank. It's not a bad thing. Make sure the temp is at least 80F and that you have an air stone, to produce lots of Oxygen for the wigglers!