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Those are baby ferns. These plants multiply producing those mini leafs with roots.
When you see the roots growing longer, You just need to cut it or separate it from the leave and then you will have a new baby fern
I will wait, just because they are still little, but ferns reproduce fast. The ferns don't even need to have the roots planted in the substrate. You can also attach them to a rock or to a driftwood if you want.