How much will the commute cost in terms of extra petrol, increased train ticket prices, increased time and thus childcare cover? Does that come to more less whatever £7K is after tax? What about the overall packages? Are there benefits like private health, or extra holiday?
How much longer will the extra commute be time-wise? I know I don't really want longer than an hour commute, but I know others who will do more, and it can depend on whether you have to do it every day or have the option of working from home, or if it's a single journey or one broken up between walk, bus, train, tube, walk or something.
What else differentiates the two jobs? What opportunities do they have for training, progression, things like that? Which of these aspects matter most to you?
If this second job wasn't on the table, do feel you're settling into the 2 month job well, getting on with the people and so on, or would you be considering you might need to start looking again anyway?
We can't make the decision for you - jobs aren't just about money alone, so you need to think about your values and what you want from work, and what you need from work and life (which changes at different life stages.)