An experience is a good place to start. How many times have you found something under their bed that they forgot about. You probably spend ages agonising over finding one and it's under their bed! Because, let's face it, we buy too much stuff that they'll tires of shortly and probably never remember.
What do they remember?
They remember the time we spend with them doing special things. They remember times where there's lots of laughter and fun involved. Those memories last a lifetime. Much better than the latest craze that will be over this time next year.