Child will learn using gadgets
If the phone is not very old, then I try to sell it so that it doesn't lie around at home. Several times I gave it to relatives who didn't have a phone at all.
I give it to children to play
I've been selling my Old Smartphones on the Cashify store from the last 2 times. Cashify provides good value than any other store. So It's better to sell it instead of keeping it at home as a waste device.