It sounds corny, but if there are children, they need a playground. For example - such. Multifunctional, where everything is provided - football, basketball, crossbars, slides, stairs and even a wooden house with a veranda. In general, everything you need to develop agility, strength and balance.
It may seem like this is too complicated, but if you think about it, then nothing special. Of course, in this case, a lot of wood will be needed. If you do not have carpentry, you will have to hire a craftsman. Still have to buy some materials. Although this is just an option, you can dream up and make a thematic platform, as well as pick up some details according to age.