Sometimes to get our kids involved in fine motor activities it has to be motivating - I call it finding their currency. For my boy, this was gifts. He loved making gifts for people, so for mothers day one year, we made a necklace for his grandma.
It was a great fine motor activity as well as a good one for developing our PAUSE button. First we used oven baked clay (similar to FIMO but we used the $2 shop option) and rolled the beads into a variety of shapes, then using a skewer poked holes through carefully, then baked as per instructions (WAITING). Then we threaded onto plastic string (easier for little ones to use than cotton).
Great for hand strength, pincer, manipulation, attention and self-control development! And Grandma now has a lovely handmade mothers day gift.