Primary School mixed classes

I have twins currently in year 3. Next year’s classes have been released.
There will be 45 x year 3s next year
35 x year 4s
45 x year 5s
The school has decided to split them into 4 classes:
3/4 3/4 4/5 4/5
Which will mean the 35 year 4s will be split across 4 classes. And those class will be dominated by the other year groups - 22/23 year 3s or 5s to 8/9 year 4s.
Am I right to be pretty miffed about this? I feel as though the classes are unfairly weighted to the other year groups and that the year 4s are going to either get bored or be completely overwhelmed.
Surely a 3 3/4 4/5 5 split would have been better and then each year group would only have been split twice. Both my kids have been moved classes, both put into a 3/4 class and both changing teachers and losing their friends. It seems very unfair on the year 4s.

This is pretty common in Scotland, well around us any way. Doesn’t seem to affect them playing etc, they will probably learn a lot from the older ones too. I’m not sure how they actually teach but it seems to work.

I would see it as a positive to make new friends etc as the school won’t do anything and by the time they go to high school probably wont remain friends with their primary mates anyway.

My school was like this growing up an it never bothered me, take a p4 for example, the way mine split was if the p4 needed a bit extra help with school work an needed some extra time on things then they went to P3/4, if they were fine with the work then it was p4, an if they were doing really good then it was p4/5, then school work was looked at around Xmas an kids moved accordingly with how they were doing

I felt like it was a good idea because you were never pressured into having to keep up with the class as a whole since everyone was in a class that suited them, so kids who needed help weren't having to keep up the same standards as those that needed pushed with harder work

It might seem a shame as an adult to see them moved an their friends moved but kids make new friends so quickly an easily that am sure they will soon enjoy their new classmates an they can always see their other friends at lunch or on break

Personally as a teacher it makes no difference to me whether a class is a mix of two year groups or not as I’m just looking at the children’s abilities. I’ve had straight classes with more range of abilities than a mixed/composite class. I’ve seen so many worried parents recently after they’ve found out their child is in a composite class and really in regards to their learning it shouldn’t make any difference.