It looks like you might have "lost" quite a big percentage of your garden to shrubbery. Where is the boundary on the left? I would heavily prune the hedge to gain a bit more space.
Where is the boundary from the tree to the summerhouse and behind the summerhouse? Again, you might be able to gain some space by removing shrubs and replanting.
How much do you use the patio? Do you need all of it? Are the tables, chairs, egg chair in the optimum places for how you use the garden/the time of day?
It looks like your garden is well played in! If you need lawn space for football practice, you might have to compromise until your DC are older. When they need less play space you can use curved borders and a winding path to lead the eye down the garden and create a feeling that the garden is larger. I would consider moving the trampoline as far back into the corner by the shed as is safe and sinking it in the ground. If your DC are old enough to play safely out of view, I would consider screening that corner with plants and have a an archway with climbers as the entrance. Once they are older, I would definitely create a small courtyard or gravel garden with a feature (eg fountain, brightly coloured table and chairs, climbers on a obelisk, bird bath) with planting so you can only glimpse it through an archway so you can't see the end of the garden, just that there is more beyond.
You have a great view over the fence to the tower/church. I would be using plants to frame it and hide the fence. The fence is a firm/hard boundary but if you grow climbers with a few large plants/small trees, possibly in planters, to make the edge less straight, it "blurs the boundary" of where your garden ends and the view begins. You could use garden mirrors to make it look like the garden extends past the fence and the mirrors are entrances.
You could do something similar with an archway/bower/feature/mirrors/living willow structure under the tree at the end of the patio, to make it look like it leads somewhere. Or in the space between the tree and the shed. Or both! Or a garden mirror behind the summerhouse veranda.
When you no longer need maximum lawn space (and have the money!), I would consider creating a separate seating area and dining area and reduce the size of the patio and lawn, with curved edges/borders rather than straight lines.