Help what do I do a Baby magpie fell in my garden

Hi, so a baby magpie has fallen out of the nest in my garden, it's still very fluffy and cannot fly but is showing signs of it's wing feathers coming in.

I'm not sure what to do. The parents seem to be near by but they haven't come down to see it or feed it in a while and we have a lot of cat's in the area and I'm really worried about it.

Should I leave it be?

I have a playpen I could put outside for it and guide it into. It has an open top so the parents could fly in and see it and it might keep the cats out? Or should I bring it inside?

I put a plate of rehydrated mealworms out for it... I'm worried the parents haven't fed him in the 3ish hours since I noticed him.