I find this incredibly touching and poignant. Every time the Doctor encounters children, this is his reaction - limitless trust, love, and enthusiasm for them. He kind of IS a big kid himself (even his psychic paper won't call him a "mature, responsible adult"). But this is probably how he was with HIS kids and grandkids.
When I was the 11th Doctor for Halloween at work, I quoted this line to some fellow whovians who asked me for some assistance. I grabbed the wife by the hand and she grabbed her husbands and we ran to the section of the store they needed to find. They loved it, an they knew exactly what they were getting themselves into. :p