If I was truly concerned I would mention what I am observing to the parent about the 'challenges' the child is facing with tripping and so forth and than add 'I am not sure if it might be because the pants are too big because I have noticed that when he wears other style of clothes his balance is much better' and help them make the connections cause well they honestly might not realize that the clothes are a safety issue for their child and posing it this way does it in a manner that is not 'accusatory' or anything just an 'observation' so to speak?

I had a client once who kept sending their child in 'cute shoes' cause well they had a value about fashion over practicality .... however the poor thing was constantly tripping and falling so on every accident report under 'action plan to avoid re-occurrence' I would write 'strongly suggest sturdy running shoes for outdoor play to improve balance' cause seriously running and playing in little 'kitten healed' shoes when you are 2 or 3 is NOT IDEAL ... and it took mom a couple nasty head bumps for her to finally go out and get some proper runners for 'daycare' and whola no more accidents