The fidget toys seem to be really big for my 4th grader. My 6th grader even grabs hers occasionally. We gave a few poppits to my 3.5 yo niece last weekend and she was thrilled with them. You can get large sets on Amazon for very reasonable prices. Other ideas:
Uno cards
Lip gloss
Hair scrunchies
Bath bombs
Small foam or inflatable balls (my boys are always throwing those around)
Stress balls
Earbuds (sometimes I see them under $5 at Target)
Slime
Fun pens/pencils
Mom to Two Wild and Crazy Boys and One Sweet Baby Girl