I've assumed SEN precisely because I've been in this position and seen lots of post from other parents who have been dismissed and fobbed off because 'sen needs'. Its a convenient excuse to try and absolve the school of accountability by laying a massive guilt trip and pretending they don't have to do anything.
Its not an acceptable excuse.
It means
a) the school are failing to meet the needs of the SEN child.
b) the school are failing to safeguard the children.
The school has a duty to BOTH. It has a duty of care to ALL child as equal parties. One party having a disability does not trump their duty of care to other children - they have to balance needs. If they can not manage one child without putting others at risk, they have no choice but to take some sort of further action.
You HAVE to challenge it, for the benefit of both parties.
It actually HELPS build a case for extra support for the SEN child. The school/authority has a duty of care to that child to meet their needs.If they can't then it makes a case for further steps or transfer of that child to a more suitable setting for their needs.
Without challenging you are leaving children in a dangerous situation where they could be hurt.
If my child was hospitalised and I knew there was a paper trail of complaint from a number of other parents citing concerns over safeguarding and this child, I would be going absolutely nuts and taking further action.
This is why I stress the need to make complains in writing (preferably email so you have a copy yourself and its existance can't be denied).
Put the school into a position using and quoting its own policies on safeguarding and asking questions in line with this about why they are failing in their duty of care to your child. The child with SEN needs is not your problem and should not be made your child's problem if the school are failing to address their needs. You should only be concerned about your own child's right to safety. If they try and muddy the water, its not ok and you stress this.
This applies even more if SEN is not present, but SEN is unfortunately used as something for the school to hide behind far too often.