I have a couple to add. Our younger ds' first trip was to DL when he was 5. He went to DL again before our first ever trip to WDW when he was 9. As we were walking down Main Street of the Magic Kingdom our first day there, he took my hand and said, "I feel like I'm 5 again!" I tried very hard not to laugh, but I could so identify with what he was saying! I said, "Yep, so do I". I'll never forget that.
On that same trip our dd was 2.5 and we thought she might be afraid of the characters. Our first night we went to Chef Mickeys, and to our surprise and delight, she ran right up to Donald Duck and gave him a hug! The look on her face when she saw Mickey was just priceless. And when first Chip, and then Dale came by, she pointed at both of them and exclaimed, "Look! Two Chips!"