This is a great starter activity if you are new to taking learning outside the classroom. This is a very simple activity to manage: I give the children a theme (this is where your topic link can come in), a time limit and allow them to use any materials they can find and off they go!
From experience, the most important teaching point is to give the children a time limit, without the pressure of a time limit the children’s attention will start to wander. Some children will start by trying to produce a ‘birds nest’ as this is what they’ve seen made from natural materials in the past. With a poke and a prod in the right direction though, these children can be persuaded to be more creative. This is a typical birds nest children might make at the start of the activity:
I have used this activity with all year groups, from R right up to Year 6. Below are pictures of the artwork my year 3 class produced last year.