There are two parts to the divorce, the legal act of ending the marriage and the financial order.
If you are agreed that you are going to divorce, and can agree the grounds, then the legal side is quite straightforward. The petitioner files the application, the respondent replies to the court papers to say they agree, then the application for decree nisi can be made and some 6 weeks after that the decree absolute. Court delays are making this process a little longer, but it can be completed in around 6 months to 9 months (max).
For the financial arrangements, you have to go to mediation first, to try and reach agreement. If you don't reach agreement, this process of going through the court hearings can take in excess of 12 months, quite easily.
The child arrangements are entirely separate to this process though - the divorce court does not rule on who the children live with or how much time they have with each parent. For that, you need to apply for a child arrangements order and these applications are normally resolved in around 6 months, unless the court has to hold a fact finding hearing where there are allegations of harm involved.
Can I clarify anything further about these timescales for you?