In previous houses we have done the safety margin by filling an area with mulch and you had to stay out of the mulched area if a swing was in motion and in another house the yard setup allowed us to put a short fence around across the area so you had to enter through the equivalent of a gate to get to the big kid area. Could also do the opposite and make a little kids only play area depending on which group you have is the largest or which age group your own kids fall into.

We have a swingset but it has the bench in the middle and two swings on side that are the rubber so even when you get hit it isnt' the same as getting clobbered by a wooden board as with wooden swings.