How to mark yogurt jars?
Some permanent markers (sharpies for example) can take multiple passes through the dishwasher while still being legible, but a quick wipe with alcohol of any kind will take it off.

For truly permanent marking on glass, engraving is the way to go. A vibrating engraver is more precise and more expensive than a rotary tool (dremel or cheap equivalent), but the latter is perfectly fine and makes wider lines. The downside is that this isn't particularly visible against a white background such as yoghurt unless you go over it with marker.

Simply twisting a bit of coloured wire around the clip might do the trick.

Plastic stickers (widely available aimed at children) can survive being washed many times as evidenced by my daughter's water bottles, but you're a bit restricted as to design - is one yoghurt a good match to pirates and the other better for princesses?