but were told their children weren’t good enough (at 6 years old) and were holding the Scottish kids development back.
This, in itself is massively out of order, regardless of any nationality issues.
At 6 years old?
We have kids who have been training twice a week and playing in games at the weekend for three years who can barely dribble a ball 10 yards. They train and play alongside other kids of the same age who are capable of launching a 30 yard volley into the top corner of the net and are being scouted by professional clubs.
At that age, at that level, this is perfectly normal and acceptable as long as the kids are having fun.
If the kids do lack skills and ability, that is precisely why the coaches are there to help them.
That’s the job. Any coach who bins a 6 year old kid because they “aren’t good enough” has failed utterly.
It’s not the kids, Polish or otherwise who are “underdeveloped” in the OP’s case it seems.