Is this rude?

My niece asked if she could have a graduation dinner party at my home, (she lives with me) anyway, I said yes, only on the invitation I want to stipulate "leave cell phones at home or off"...the last time I had a gathering here everyone did nothing but TEXT back and forth.

I don't mind spending the money or doing one hell of a lot of work so I don't think it's asking too much to please socialize, dance or whatever.

Thoughts?