Nollie has always loved to tie things up. Initially if she found a belt or a watch that wasn't attached to a person she would wrap it around and through itself so many times that it looked like a ball. She's now moved on to tying anything she can find.
I have started giving her a shoelace to play with and she will sit quietly for half an hour or more and just tie it up.
If there are beads about she will add them.
Look at this little diddy she did on her dress strings.
I'm happy to encourage anything that will keep the kids busy. This doesn't seem to be a fleeting obsession so I'm on the look out for ways to keep her excited with knots. She's a bit young for a knot tying book so I guess I just keep her occupied with an assortment of items to tie up.