Talk to his/her parents, but show some empathy. If you don't know for sure don't accuse, just ask.
If the kid is just 4 years old I'm pretty sure he/she might not get the concept that toys aren't for playing with.
Also if he/she comes over often make a special shelf(or box) or something of toys they can play with similar to what they are interested in from you.
For instance if it is Lego they like pick up a $15 Star Wars army builder pack, or an inexpensive Marvel set that is just for them when they come over.
