Tadpoles in wheelbarrow?

While we were on holiday our wheelbarrow filled with rainwater. It had a sort of ramp up to it where a piece of cardboard had fallen. We have seen our resident frog(s) a few times of late in the borders, despite the fact we don't have a pond.
Today we noticed (what looks like) tiny tadpoles swimming round in there, followed by a frog popping his head up to say hello! However, surely it's too late for tadpoles? The wheelbarrow is in a small alleyway sheltered by the garage and another wall. Gets some sun in the afternoon.
Will post a picture tomorrow if anyone is interested? Any advice appreciated as to what to do. We've kept the ramp so mister frog can get up and down.

 

Blimey, that is a bit late. You sure they're tadpoles and not Mosquito larva? Frog might have been feeding on them.

 

Hi Zig

Before reading your post I thought the same as you Mosquito's

 

Thanks all. No sign of mr frog today so decided to tip it out as I'm allergic to mosquito bites.