There isn't a set answer but typically from what I have observed as a professional working alongside the police is that what will most likely happen is:
After you report it to the police he will be arrested
After he is arrested he will be advised of the allegation you have made and will be interviewed in relation to this. If he has legal representation during this interview he will be told not say much.
After the interview he will be bailed - usually for around 28 days not to have direct contact with you. Unless there is a risk to the children it will be expected he will still be able to have contact with them through a 3rd party.
You will be asked to complete something called a DASH risk assessment and depending on the score from this may be referred to a multi agency process called MARAC where the risks to you will be discussed and actions given to various agencies to support you. Most likely a local domestic violence charity or victim support will contact you.
After that it depends on you what you want to happen to a certain extent- if you don't support a prosecution then the CPS might tell the investigating officer that there isn't much they can do. Bail conditions will end. That might also happen if you support prosecution, but it might not and at some point you mught have to go to court. You will be offered support through Victim Support around this.
If what you disclose to the police is very serious then they may consider prosecuting without your support if you dont give it but it's not that common and usually only happens when the police have a lot of evidence from other sources.
After the bail conditions expire if you feel at risk still and don't want contact then victim support/ IDVA will support you to apply for a non molestation order
His contact with children if there isn't considered to be a specific risk to them from him will be determined by childrens services / court depending on how far he pushes it.
That all sounds overwhelming and scary and it is, but I've seen so many women survive and come out of the otherside of these processes and flourish. You won't regret it at all once it's over and done with but it's not an easy journey. The support is there though and I urge you to take it.