Last night, my daughter announced (after putting toys away) that she had too many and asked whether she could give some away. Now, we have trimmed things before . . . about 6 mos ago, at my initiative and she was included. I was very proud of her for making the suggestion. She would even ask who gave her the item, so, if it held sentimental value, she might opt to keep it. She wanted to give away almost all of her wooden animals. I had to nip that in the bud, though, as she has a younger brother who might want to play with those. Otherwise, she decluttered several stuffed animals, dolls and a very much loved dolly umbrella stroller! 
