Learn thru play???

With the house flooded with toys, they are basically playing every single moment except when they eat, sleep or bath. I certainly hope what people say about "learn thru play" is true.
Recently I realised that they had started "make-believe" playing. I caught them pouring "water" from "cans & jars" into "cups" and "drink", frying with "forks, spoons and pans" then feed themselves, each other or us, pushing the trolley in & out of their "house" and went to "market" to buy "vege" & etc ... Though silly as it may be but we still join in, hoping that they'll develop creativity skill thru imaginery playing.