It can be hard for younger children to understand the importance of keeping distance between people outside your own 'bubble' while getting outside. We've had some ideas from parents in our team on how they keep kids close by when needed:
1. Announce different formations when you need to get in line to pass people by - shortest to tallest, oldest to youngest, who has the next birthday, etc.
2. Expend extra energy by having kids complete a quick exercise before having to come in close again - 2x starjumps, hopping on one leg, or completing a running circle of the bubble.
3. Having a 5-step rule - staying no more than 5 steps away (especially when there are a number of other people about).