Murmuration's advice is very good. I too have had to cut down on all hours working, for my own health and because of children/other responsibilities. I work about 1/3 less hours than I used to, but am much more efficient as well as utterly ruthless about what I can and can't do. I always have one day off a week, and work only 3/4 hours on the other weekend day if I have to.
There are times when it's almost impossible to constrain hours- I would say if you are putting in a grant against a deadline, or sending a paper back against a deadline, or possibly a peak of marking. This isn't every week though- and as you say, you are becoming less efficient over time through exhaustion probably. You really can't be concentrating if you are working from early morn til eve. Do you really mean childcare from 6am to 7pm? I don't know if I misunderstood or you meant one hour? If it was 13 hour days, that's ludicrous as a long-term way of working.
Also, how old are your kids? If they are small then no amount of efficient working can compensate for the time and energy suck of small kids! It's unrealistic to expect that you will be able to produce amazing work in every area with little ones, the good news is they grow up and your opportunity to refocus on your career will come.
Can you talk with your HoD or another senior/mentor figure?
I do the things I would be sacked if I didn't do first- so that's teaching well, answering student emails (v briefly and I have lots of tactics and FAQ to divert the quantity here), marking and getting through the teaching term. I then focus on the most important research things- so writing REFable papers/required by grants, and writing grants. Do only one at a time, focus on that instead of switching between projects constantly (if you are writing, anyway, I can't write 4 papers at once, some may!) Then everything else- being the best committee member, joining in away days/seminars, editing journals, running conferences and so on- it happens if it happens but if it doesn't, it doesn't. Put it in the list of things you will do when you are less exhausted and your children are older. If you are on probation (which isn't clear)- do those things and only those things. Protect your own mental and physical health.
I don't care if someone comes on and tells me I'm a bit selfish for not doing all the 'extra' stuff and someone has to do it- it's that or essentially lose my job and sanity. Universities have been increasing workloads for a long while now without any recognition of what this means in terms of stress for academics - double the students, twice as much feedback, more REFable papers, on it goes. Amidst the madness, you have a perfect excuse to keep yourself sane. Go for it!