Straws are good toys, string is fun, together they make a different toys. The straws provide a more random motion because they’re stiff except at the bendy zone and between straws. It fits all five at once and each kitten’s actions affect the straw for the next one down the line. Also, there is little danger that they can get tangled in it or swallow the string (which can be deadly or costly, and definitely not fun).
To make: get 5 or so plastic straws and about 5 feet of yarn or string. A bobby pin makes a good threader if you flatten out the open end. A metal tapestry needle would work too. Tie the string to the bobbypin and drop it through the first straw (shaking it can help the pin exit the straw) and secure the end, either by tying to a button or jingly bell or by cutting a hole near the end of the straw, threading through it and knotting. Add more straws until you’re almost out of string. Secure the end (maybe a different method than the start). This all will be easier if you are not around kittens.
Below, I added their growth chart. Some likely will be ready by the 24th, some won’t. (Weight in grams, ~950 for the 2 pound goal.)