heh, my almost 4 year old cramps my style and she’s been living with me since her birth It would certainly be an adjustment to aquire one suddenly for a few days.
Can he use scissors? Give him some child-safe scissors and some old magazines to cut up (might want to keep him in view while you do this so he doesn’t decide to cut up something else instead)…
Any parks nearby? He could run off some energy and you could position yourself nearby and read/call someone/etc…
Water is always good for fun at our house, either a bath at an unexpected time, a tub or bucket of water in the backyard if it’s warm enough, or at the kitchen sink…give him various plastic kitchen tools, bowls, and measuring cups for toys…
My 4yo likes to “bake a cake”—basically flour and cinnamon in a bowl which she then stirs, transfers to another bowl, etc. Makes quite a mess but keeps her busy for a while. Add water for instant goo.
Speaking of goo, find a homemade play dough/glop recipe on Google. He can help you make it and then play with the results.
Go to the library and check out some kidvids and books if he’s into that. Our library has puppets and activity kits you can check out too. Or maybe a book on tape…I got out my old boom box and put a green sticker on the play button, a red one on the stop button, and a blue one on rewind and she kept herself busy for a while that way.
Go to the thrift store and buy a bunch of cars/blocks/whatever he’s into. Then he has some new toys to play with but you haven’t spent a bunch of money.
New foods (combined with the abovementioned video from the library) can keep my daughter quiet for a while. Buy him a box of that Shrek cereal or some obnoxious fruit snacks (heck, you don’t have to pay his dental bills, right? ).
I hope some of these are helpful…my daughter is a pretty quiet “sit and look at books” kinda kid…if your nephew is a “run around and explore everything” kinda kid he might find my ideas totally dumb.