How to identify wool vs acrylic knit items

[tricia17lee]

So I found some more possible CD items posted on an online thrift store group local to me. They are selling them as warm baby items- but it looks like someones CD stuff- wool longies, soakers, and fleece. When I asked about whether they were wool or acrylic the lady wasn't sure but didn't think wool. How could I identify this? Can you tell from pics? What would I look for when feeling the yarn?