I've just written a 20,000 word novella in the time given by 2 mornings a week of preschool, less exercise whuch cuts into both those sessions (but need the exercise for my back).
You're more likely to value the short sessions (and can mentally plan things at other times.
Moreover, you know that you'll get lumbered wirh some non-writing donestic task (paying urgent bills, doctir's appointnent, etc.), and how gutting would ut be fir that to fall on one if your writing days?!
Your leisure centre shoyld have a crechr, and may run out of term activities fir older ones (supervised), which you can make use if if you're in the habit of concentrating for short periods.
Yes, you'll only get it done if you make it an absolute priority, to the extent that if your friend who lives abroad who you haven't seen for years is in town that day you still have to say 'sorry, I'm busy'.
In some ways I find it easier to do that with a weekly writing day rather than daily few hours. A fortnight is a very long time between sessions and I remember being absolutely panicked at the thought of losing the thread.
Or choose the year-round full days until the summer holiday is out of the way, and then switch to the "preschool" option? Presumably you won't be paying for the "preschool" style childcare until you are using it, so it's just a juggle.
Unless waiting lists are a problem and you would have to take up the "preschool" option now, or lose it?