As I posted on another thread:
The selection of years will also be to gather data and to experiment with 'what works'.
Year 6 do not have an enormous amount of 'formal curriculum' left to cover, so time can be spent working out how to transition children of that sort of age back into schools, work on counselling & support, work out the routines, processes etc that could be used for the whole school without the constant 'but we also need to cover x.y. and z' that would be the case for other years. Because they are the oldest children in the school, they can be models / mentors for other years to show the new expectations and procedures if / when they return. And statistically, data from how much they increase R can be applied with some confidence to e.g. Y5 and Y4.
Yr and Y1 are the most difficult to educate from home, and are absolutely the worst case for social distancing - so again, if having them in school can be done without an epidemic amongst staff or a huge rise in R, then it's a reasonable bet that other year groups will be less risk.
So there is definitely an element, it seems to me, of choosing 'guinea pig' years to inform statisticians of the likely effect of returning other year groups."
So if this works, they yes, Y2 will go back. If it doesn't, you might be very glad that Y2 wasn't in the initial wave...