Children don’t like change. They haven’t it experienced as much as you have and don’t have as much control over how things change as you.
Keep change to a minimum. Create a new routine for the children as soon as possible. Whatever arrangements you make with your partner, stick to them. Don’t set radically different boundaries around behaviour than your partner, this is likely to confuse children and make transitions between parents very difficult. Keep things civil with your partner in front of the children and don’t diss her behind her back.
Children may refuse to believe what has happened and try to get you back together. This can be a danger sign. Think about how they’re going to feel when they fail to do it.