I dont understand why your dh is spending less time with you. DH is a very long serving officer but in a specialist unit at the moment. When he used to be on shift and the children were small he had plenty of time with them.
Early shifts are just bog standard 'normal job' type commitment so I would write those days off. When the dc were school age this is the shift where both before and afterschool care would be needed. DH started too early and finished too late for childcare drop off so this would have been down to me on this shift.
Lates my DH would get up and about in the morning, take the dc to the park, swimming, do some shopping. Then after lunch he would head out to work. At school age he could look after the dc in the morning and do the school drop off. Then he could go to the gym if he wanted to. I would have to do the evenings.
On a night shift (my favourite because I get the bed to myself) DH would go to bed and get up around 2pm. He could take the dc to the park, shopping etc. He could put the dc to bed, cook dinner, loads of things. Once the dc were at school he could both drop off and pick up.
Then he gets his 3 or 4 days off which is when we used to go away for short breaks because its almost impossible to get any sort of leave
However I will say it is damn hard. People dont understand why you cannot commit to working/volunteering/going out the same days each week. They just dont get that the shifts dont fit that way so its very hard if you need flexibility in your life. Friends tend to stop inviting you round for a weekly chat on a Friday because you need to be home for your dc. Some people object about your DH job and will ignore you or cause issues for you. Eventually only other people in similar circumstances actually understand. But they tend not to mention it so its difficult to find people like that.
You need to decide if you are happy to continue living the way you do. My DH has been on his unit for around 9 years now. Sometimes he doesn't come home for days on end. Manchester arena attacks the other year, I barely saw him for 3 weeks. The olympics in London, I didnt see him for more than a month. When he gets home do you think he wants to sit and chat about Eastenders or soft furnishings? No, he needs a few days of unwinding, usually it involves mountainbiking or kayaking or something. I give him his space for those days.
I dont think your DH has been in the job long enough to have an efficient way of winding down. He is still being judged on his performance at work and his job is still very much on the line until he has passed his probation period. At home he has 2 very small children and a partner who doesnt yet understand how much being in the police messes with your head. Thats a lot of stress for him, but he is taking the piss a bit with going down the pub and gym 4 days.
Your dc will be fine, its normal to them for their dad to work this way. Its only you who will understand it is different to a lot of careers.
You need to decide if you can continue living this way. If not then put things into place to leave. Go and find a 9-5 man who you know will be home in the evenings and weekends. I can guarantee life wont change while he is in the Police you have to change to fit around it and not many people are willing to do that.