I tried to run the double slit experiment at home for my kid with a cheap red laser pointer. I partially covered the laser with four pieces of electrical tape to make a tiny square hole. To my surprise that was enough to get a cross shaped interference pattern on my wall with a splatter of other dots around it.
When I covered the hole with a single hair strand I did get the nice classic new line of interference (perpendicular to the hair).
The "why do I get the cross beforehand" seems to be answered here (How can a single slit diffraction produce an interference pattern?) that unfortunately I only partially understand. Is there an easy way to fix this? Is my laser not producing "coherent enough" light and I need a different light source? Is the hole still too big (too small)? Would it help if I managed to place the slit further away?