Yes, anything that isn't their feed needs grit to help them grind it up for digestion. Well, other than soft stuff like yoghurt or scrambled egg.... But mealworms, definitely. Or peas, or bits of shredded cabbage or carrots, or grass clippings.
I just use construction sand - a 50# bag from Lowe's is pretty cheap and you can use it for other things in the yard. (Like a dust bath in a plastic kitchen tub, in the coop, during rainy weather.) Not play sand, it's too fine. All purpose or "consruction" sand with little bits of granite and pebbles in it.
Just put some in a small plastic container with short sides. They'll eat it AND play in it.
