I have grown Whippersnapper a lot of times. Don't prune it! But give it a larger pot - the more tomatoes you will get. The large pot in your pic is okay, but the three smaller ones, no... The pots should be high enough so that the plant can tumble a bit.
BTW my eldest granddaughter likes Whippersnapper best when the tomatoes are still pink, fully ripe the tomatoes are red.
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