Should I drop this client?

Hi all, a bit of a rant but also, what should I do, is this acceptable or unacceptable?

Been cleaning solo for years and years, but dropped the business then re-started last year. I'm in London, UK, but finding that the market is saturated for cleaners and clients won't pay a good price.

One of my new clients I've been cleaning for them for 6 months:

Young professional couple, both working super-busy jobs. Two small boys under the age of 5. I clean once a week, 3 to 4 hours, paying £55 to 70 for the job.

4 bedrooms all with double/full beds, need changing (duvet covers), 1 bathroom, large kitchen/dining always with food dropped everywhere and clutter to move around or pick up, stove full of dripped food, two huge reception rooms, large hallway upstairs and down, take out trash, empty their two vacuums after using.

On my initial walkthrough, the house was picked up and clean. Stove top sparkling, nothing cluttering the floor. Client made it seem like a quick breezy job, and it looked that way to me too, even though physically large house, looked like they kept it clean and picked up, so that topic never came up (picking up tons of stuff).

The mess has been worsening steadily. NOW, there are always toys, books, Lego bricks, used Kleenex tissues, used DIAPERS/nappies on the floor of most rooms. I have to spend almost 40 minutes of the 3 hours just picking up. Client NEVER picks up before my visit.

Stove top, sink and all kitchen surfaces covered in dried food that was never wiped up after cooking. I'm only there once a week so some of this should be client wiping down, but they don't.

They are nice, friendly people so I know there is no malice in this - they're just super-busy with demanding jobs plus two very young children. Grandmother helps with childcare but not cleaning. But I feel taken for granted and casually disrespected because of the all the mess they leave. Last straw was my broken duster.

Last week I forgot my duster, left it behind as I was stressed about getting things finished - she wants just three hours for all of this work and doesn't like it when I run over and have to invoice a higher charge. They make great money but they don't like paying me for more than 3hrs.

I assumed that someone would find my extension duster and just hang onto it for me until next cleaning. Today I found it snapped into two pieces, lying on the floor amid toys and other clutter in the doorway of one of the small boys room. They clearly been playing with it and broke it. It's metal and the broken part was jagged and could have hurt someone.

It was entirely my mistake to forget this piece of my equipment - I don't make a habit of leaving things behind! I was tired and rushing to finish in 3 hours - but am I wrong to have hoped that a grownup would find it and keep it for me? I have to not break their stuff, but they broke MY stuff!

Low pay, casual disregard, house being left dirtier and messier each time - do I politely let them go? I think I know the answer but I just needed to get this off my chest.