What are they doing when they are clunking / popping? Is it only certain movements, or all the time?
From my understanding, there are two things that this could be (but by no means am I diagnosing!):
1) fluid in the hip joint itself essentially “popping”
2) the hip itself moving too much in the socket due to instability (weak muscles / stretched ligaments)
I don’t believe you want to exacerbate the poppingany more than you have to (if it happens when they walk, we can’t tell them not to walk!), but rather try to minimize through stabilization exercises and paying close attention to whether or not they cause pain or discomfort at all.
I’ve had a client in the past that had a similar challenge – we worked a lot on the abdominals, back and on hip movements that did not cause the popping, which eventually strengthened her body enough that quite a bit of the popping reduced. She had gone to her doctor who said in her case there was just extra fluid and that it was similar to cracks anywhere else in the body-that you don’t want to force it, but if it happens naturally, just to let it happen and worry if it causes pain. I do know others who have their femur pop in and out of their hip who have later sprained it and had to rest for an extended amount of time.
Hope this helps in some way!