Apart from the free Year 4 maths assessment, there are also Year 4 NVR and English assessments.
There are also plenty of free maths worksheets (sets A to D) that you could try with your Year 4 child – see
There are a number of workbooks in the shop that may be suitable for Year 4 – ages 9/10 rather than 10/11.
The exercises and practice tests/past mock tests in COAsT are mostly aimed at Year 5 pupils who will take their 11+ at the end of Year 5 and just at the very start of Year 6. You may want to stretch your Year 4 child and try some of these.