Don't fret. You're investment hasn't been wasted. There are still hours of fun to be had from this play equipment, but your children need a little help reengaging with it.
Your children have become accustomed to seeing this play equipment everyday in their garden and as a result they don't really see it.
This happens to adults too. Perhaps you bought a cupcake maker, and when you first got it you enjoyed making batches and batches of cupcakes and decorating them in elaborate styles. And then one day, you put the cupcake makers away and forgot all about it. Even though you see it every time you open the kitchen cupboard you don't think to get it out and use it. And then something, a memory, a photograph, or a comment from a loved one, jogs your memory, and you remember how much you enjoyed using that cupcake maker, and you start using it all over again.
Or chess. Do you like playing chess? But why has it been so long since you last played it? You sort of just forgot how much you enjoyed it didn't you?
Are there times you have taken a neglected toy, that has been untouched for months, and hidden it away. Then the next time your child sees it, they are more eager than ever to play with it (this is usually right about the time you are trying to through it away).
Sometimes obvious things get forgotten about, until they are put away and then rediscovered.
This is why toy rotation systems work so well, as periodically toys are hidden from sight, and then rediscovered when it's their turn to be out.
However, with big outdoor play equipment, it's not possible to hide it away for a while.
Instead, you can inspire play ideas with your own catalogue of garden activities.
Make a list of all the things your child has enjoyed doing in the garden, ideas you have seen that you would like to try out, like the soldier training ground acitivies, and toys and play equipment they enjoy using.
Now photograph the equipment, or the game in progress, and use the images to create your own play catalogues, which you can use to inspire play ideas with your children. Before it's time to play outside, sit down together and flick through the photos to help you decide the games you want to play.
You can use a simple ring binder to keep the images together. Storing the pictures in this way will help you adapt the catalogue to suit the situation. For example, if you want your child to play independently in the garden, show them only a selection of games and activities that are suitable to play without adult help. Or if the weather is cold, take out the images of unsuitable activities like water play.
As your children grow out of the activities, or no longer need the system to inspire their play, you can keep the photographs as a reminder of the games they enjoyed when they were little.