FLOWERS LOOKING LIKE POPPIES

I had bought my mum two pots of the above plant last year and now there are many such plants growing in her garden.  According to my mum, she doesn't need to plant them.  The seeds get dispersed and new plants sprout out.  Since I have yet to pinpoint the actual name of the plant, my mum calls them the false poppy flower plant since the flowers look a bit like poppies.
Is there anybody who can tell me the name of this plant?