My old pond sprung a leak a year or two ago, probably caused by plant roots piercing the liner. Hence no longer contains water. I would dearly love to have frogs again, and am wondering if there is a minimum size of "container" which would allow wildlife to live and thrive.
Something as small as a basin will have visiting birds and frogs.
frogs will come back even if there is no water. Any water will do. an old dustbin lid, a kitchen washing up bowl. anything
I'm going to take your question very literally, 'which would allow wildlife to live and thrive' - though frogs may make use of the smallest containers for them to live and thrive perhaps consider restoring the pond?
I know it is daunting but I left mine for many years when it went the same way and regret each lost years now. Having it back now makes my garden feel right again.