we could be in trouble

This week my son came home from school and asked if he could go to "Trudy's" house. Trudy is not in his class, and I don't know her last name or her parents.  In fact, I'd never heard of her.  Turns out my boy knows her from recess.  And so my hubby and I told him that it wasn't likely we could take him to Trudy's house to play that day.  He was not deterred.  He pulled out a piece of crumpled, folded paper from his pocket and boldly pronounced, "But I got her number!"

After my husband and I recovered from the fit of shocked laughter that struck us, we studied the piece of paper. Trudy had invited him over, and had written her and my boy's name on one side, and on the other, her street address.  

Anyone ready to walk me through this?  Thought I had a few more years to prepare up in here, before the little ladies started giving my son their numbers to stick in his pocket.  

I thought you were a toddler, like, yesterday.
At least Trudy has great taste in playmates, I'll give her that.