If you let your kids use them and moderate their use they won’t feel like they have a “void” in their life, that they are missing out on something. Once they have this feeling of a “void” you never know what they will do when they are by a friends house.
I heard of a story of two parents who never let their kids have soda. What do you think they did by parties and kiddushim when their parents weren’t there? They drank soda as if there was no tomorrow. Is that better than restricting soda to only Shabbos?
Let your kids get these gadgets but make them earn its use and keep on top of them. I could think of much worse things that kids could be doing if they are bored and don’t have these gadgets.