I think you've received a lot of good advice on this thread and I agree with you that things do need to change. I also work full time and during the week I tend to do the bare minimum of housework (but that doesn't mean nothing at all). Weekends are when I do laundry, change bedding, deep clean the kitchen and bathrooms, etc.
IMO children (and adults) need a bath or shower daily, and bedding should be changed once a week. Though of course some people would say this is too much.
My best advice is to keep on top of things. You need to get the house into the state you want first, obviously. But once you've achieved that, it's so much easier if you maintain that standard with daily/weekly tasks. If you clean the bathroom thoroughly once a week, it shouldn't take more than half an hour. But if you let it slide and avoid cleaning, once you finally force yourself to do it the job will take much longer. And in the meantime you're back to a depressing, dirty room.
Other bits of advice that have helped me: keep cleaning supplies where you need them. So everything to clean the bathroom is kept in the bathroom, etc. I used to have a central location for all cleaning supplies but it's so much better to store them where they will be used.
For decluttering and general tidying: as you're sorting objects, touch each item once. So if you have a whole load of things, put each one directly in its designated home or throw it away/recycle it immediately or put it in a bag for charity shop donation. So often people compound the issue of clutter by just creating more piles of things and then basically moving them around without actually solving the problem.