If DH had a POA over Health can he arrange a Care Needs Assessment and be there when they visit to do the assessment. Unfortunately lots of people with dementia won't see that they needs help and will tell the SW that "it's ok, DDIL does that". DH and you will need to be firm and tell the SW that you can no longer give that level if care as she had become violent with your young DC.
At the Assessment you should be able to discuss things like getting her into daycare for the 3 days a week that you are visiting currently. You'll probably need to be firm and insist that you can no longer be there with your DC as she is a risk to them.
I'd also be reluctant to agree to her having a care line installed and you put down as the contact. If she needs help overnight regularly, this shouldn't be automatically provided by you. Remember any care that you agree to providing could continue 365 days a year for years to come.
If you want to pay for some care while you wait for the assessment, some care home do offer daycare and one local to us even offers transport.
As mum5net says, call the Attendance Allowance people and get them to send you the form. Once you've been granted the allowance it will be back dated to the date of the phone call.
I'd also fill in a Herbert Protocol. This is all of the information that the Police will need if she ever does go missing and it's all in one handy place with photos.
The This is me document is also useful to fill in and keep on your phone. It's a document about her life and what she likes and dislikes so that it can be given to carers and the Hospital if she's ever admitted. We sent a copy to the Hospital Ward when DMIL was admitted with delirium and then to the Care Home when she went there.