Now that's what I call weird

I found these lying on the ground under an oak tree. They look like white currants, or miniature grapes, firmly attached to the leaves.
I took them home to photograph, and if I were brave enough I'd keep them to see if anything hatches. Unfortunately I'm a Croydon girl, not very up on nature study, and not at all brave.
So - what on earth are they ? Or have I just photographed baby acorns ?