Wouldn’t recommend it. There’s a saying that “the pineapple eats you before you eat it”, which is actually the enzymes present in raw pineapple that’s doing the eating of us. Babies would have a tendency to want to suck the pineapple slice, so it’s not exactly beneficial to leave the enzymes lingering in the mouth. Try other fruits like bananas, apples or oranges instead, but of course make them into baby friendly pieces.