How to explain during my PDR I don't really want to progress

[Chathamhouserules]

Help wanted to for how to phrase this in my PDR without looking like an unmotivated slacker please! I'm very happy in my job and I want to do it well, and I'm keen to learn new skills and better ways of doing my job. But I don't really want to progress further than I am now in my career. Maybe in 15 years time (but I'll be eyeing up retirement by that time to be honest!) But I've got three smallish children and just don't feel I have any major career ambitions. I'm middle management (manage small team, have autonomy over running small projects) in HE. So in my PDR there's a bit about future aspirations and I was going to emphasise how I want to improve my skills within my current role, but how do I say 'but that's it' without looking unmotivated??? TIA!

When you are a manager you are supposed to be aware that people on your team are happy in a holding pattern. But you should never take it for granted that this is always the case.
A decent manager will recognise your current views but needs of the business might mean you will be asked to be part of one-off projects based on your experience.

It's all about the phrasing... I talked a lot about work/life balance and how wonderful that my present role allowed the flexibility I needed to give my best in both aspects of my life, that my concern in going further at present would be that my performance would suffer, that I would love suggestions about how I could give the organisation more value within my current role...