It totally depends on what you and your wife are like. Are you roughy-toughy types, or more suburban types who just enjoy your house and garden?
Animals such as sheep, or geese, are a good idea if you actually want to keep them, but they do require care and some fairly hard work to look after. Overall, I would say that keeping animals on the land would be much harder work than zipping round weekly on a ride-on mower, or tractor mower.
As you already have an area left wild for flora and fauna, and an area of woodland, perhaps you would like to use your 2 1/2 acres to plant up with mixed native trees and flowers to increase that available area for wildlife. If you are involved with the community, then you could turn it over for wildlife managed by them, or for private vegetable allotments. There are usually people who have no garden of their own, but who are desperate to grow food for their families who would jump at the idea. Perhaps less so if you are in a very rural area.
Going back to when you bought the land, what was your reason for the acreage, or was it the rural setting and the house you went for?
Are your grandchildren active types and do they visit often? If they have bikes, then you could set up paths and a course for them to tear around, its complexity depending on their ages. Your neighbours would either love or hate that option, but it's not as if it would happen every day, and they may love watching the children play. You could extend it with paths through the woodland if it was a success. In fact cutting a winding path from your house through the woodland to the grass field could make you use it more, and it would be more of an adventure for your grandchildren to explore.
You could use it as a 'glamping' site if you want to make some money from it, although I can't imagine that would be popular with your neighbours unless they were involved somehow, for example selling home baking to the campers. As you both work, perhaps that's an idea for the future.
Not knowing you, where you are, and what your aims in life are, I can make no better suggestions.