Have a go at this rainbow challenge.  Pentagons see how many colours you can do.  Hexagons you could try any or all of the colours or get an adult to change the numbers and try adding/subtracting to 20 and numbers up to 100.  I tried this with my little girl and found it easiest to read the PDF myself.  You could try one colour each day for a quick mental workout.

https://www.bbc.co.uk/teach/school-radio/cloud-rating-1/zkgt7nb