Hi, I am working towards a masters & have a full time job and special needs DC...not quite there but have completed most of it/passed the majority of the modules so can only speak from experience as to what has helped keep me on track.
All your energy needs to be concentrated on what you have on your plate (work, DC, studies) so don't waste time feeling jealous/guilty/resentful or whatever. Tell yourself that you will study for a period of time that is not too dauntingly long (say a couple of hours at a time) then will give yourself a break. Even half an hour during a lunch break etc can be really productive. Short intensive study periods are a good way to go and fit best with the multiple demands on your time.
You don't mention whether you have a supportive DH/DP but now is the time to enlist any support you have whenever you really need to get some study time.
I don't know what your discipline is, but presume that you have your dissertation topic and that you therefore know what you will be writing about, what you are aiming to accomplish and roughly how you are going to approach it. Breaking it down into manageable tasks as Lomaamina suggested, is great advice.
When I did my dissertation I kept in mind: the purpose (what I wanted to accomplish, the problem/s I was aiming to solve); the content including research outcomes etc, anything which was relevant to the purpose, the 'story'; and the structure, ie how to tell the 'story' in a clear and coherent way.
I focused on these 3 - purpose, content, structure - chipping away at each of them a little at a time until finally they met.
Don't wait to feel motivated - just get started even if you tell yourself it is just for a little time. Once you are started, you will get engrossed and once you have invested some time and effort it will get easier & easier to keep going - especially when the end is in sight. Good luck!