Well, school is often boring for a wide range of kids. It's hard for them to get the right balance for every kid. I have a very capable kid who gets bored. He's not given work that's too easy, he just finds work boring! School give higher level work sheets to stretch the kids. The other child finds some things easier, some things harder, but all learning is "boring" apparently.
For my eldest there is not enough sport and too much English. For my youngest there is not enough music and play time, and too much maths
For your kids it sounds like there is not enough academic work at a high level.
There will always be something there is not enough of, at every school, for most kids.
Unless the school is v poor, or your children are brighter than the brightest kids in the year above, then I'd just leave it. School is generally, sadly, pretty boring for a lot of kids. It's about teaching them how they can find some interest in what they are doing. If the maths is too easy, suggest to them they tell the teacher in that particular lesson and ask for a higher level worksheet, or suggest they use the time left over after answering all the easy questions, to start writing down their own maths problems or paying some maths games on paper. If English tasks are too easy, encourage them to be more creative, find what part of English they are weaker at and get them to focus on that in class. If they are writing a story, ask your kid what would make that story harder and encourage them to practice next lesson.
I'm of the school of thought themat there is something to be learnt in every situation. If school was boring today, ask kid to keep a diary of what was boring, why, and what they could have done differently in that situation to make it more interesting for themself.
If your child is genuinely exceptional, so outperforming the children in the year above, maybe they need to move up a year.