The government model (at the minute) works in ‘pods’
1 adult to 15 children. Pods do not mix. 1 person in pod 1 becomes ill, then pod 1 goes home to isolate. No other children or adults will have been in contact with that pod so they won’t be at risk from pod 1.
This will be the same model used regardless as to wheather you are a key worker or child in EYFS, yr 1 or yr6.
Obviously if you have a key worker child in yr 6 (for example) their pod will be made up of other year 6 pupils rather than a mixture of year groups.
Key worker kids will be at no greater or lesser risk if people choose to keep their EYFS, yr 1 and yr6 pupils at home.