A good way to avoid this kind of thing might be to treat your nephew like a valued family member and even a friend, rather than a criminal.
I have 4 nephews between the ages of 3 and 7, and they have never been a problem around my collectibles. I make them a part of expecting and opening new pieces and give them some small pieces for their own. They've turned into appreciative, responsible, and even savvy little collectible experts.
The only people I have to worry about are the adults who come over and start grabbing things off shelves like fools.
I also find the impulse to get into a pissing match and taking or breaking things that belong to a 5-year old very disturbing. Way to set an example.
I have 4 nephews between the ages of 3 and 7, and they have never been a problem around my collectibles. I make them a part of expecting and opening new pieces and give them some small pieces for their own. They've turned into appreciative, responsible, and even savvy little collectible experts.
The only people I have to worry about are the adults who come over and start grabbing things off shelves like fools.
I also find the impulse to get into a pissing match and taking or breaking things that belong to a 5-year old very disturbing. Way to set an example.