My 3 year olds struggle with pica
My son saw another toddler eat a crumb off the floor at a family gathering when he was about 9 mos old. He tried it and realized it tasted good and started eating little spec of dirt or string or whatever from the floor after that. He was also a chewer, which may have started even earlier. He chewed a chunk out of his crib. He would chew the pages out of board books. He chewed a windowsill of an old home which raised his lead levels pretty high! He did eventually stop chewing everything, but then he started chewing on his shirt, biting his nails, grinding his teeth...something always replaced it. He bit an eraser at some point and realized he liked it. That was a struggle that continued for about a year until he was about 7. I haven't noticed him eating anything unusual since then.