Our son had a slight cleft palate, not visable and only picked up once he was 4/5 after he’d had some speech theropy and other tests.
Basicailly he just sounded a little nasally, unless he had a cold then he was a little difficult to understand for some people.
After tests it showed that 60% or so of the air was coming out of his noise when he spoke (hence the trouble understanding him when he had a cold). He had an operation which simply moves the muscles back a bit to create a better seal when he speaks.
He improved down to c.20% when he was last tested a few years ago, but we took the decission to not put him back through a repeat operation (pretty common, but we was not made aware of multiple Op’s prior to the first). For a few reason’s, mainly he was still re-learning to speak now through he’s mouth (this is still ongoing) and secondly he’s still growing so the gap could get larger through he’s teens, so there was no guarentee that there would be more to follow.