Where do you live? I live abroad in continental Europe but would happily come and help you out if I lived near you. Bet loads of others would too! So don't be afraid to ask for help! (Cleaning/sorting someone else's house is always much more fun than doing your own.)
Could you confide in a friend and swap childcare and give one another a free day? Are there any single parent groups near you that you could approach?
Failing that, start with flylady crisis clean
(ignore barftastic language of site, the underlying system is sound)
www.flylady.net/d/getting-started/flying-lessons/crisis-cleaning/
Then tackle zones - just 15 mins a day makes a difference - but you can't clear clutter so use those 15 mins initially to get rid of stuff. Once you have decluttered, the cleaning is much quicker.
Three boxes per room : chuck, charity and keep, timer on for 15 mins - see how much you can do in that time. But remember to chuck out rubbish straightaway, take stuff to charity shop straightaway and put away stuff you are keeping straightaway. Otherwise toddlers get in to the boxes and chaos reigns again.
Spend one day going through your clothes and chucking and sorting
Spend another day going through your toddler's clothes (ditto)
You will be eating an elephant one small bite at a time in other words
And do basic routines daily ie one load of washing a day, dried and folded and put away, wm (and dw?) on in the morning (or night before, and emptied, bathroom wiped over quickly once a day etc etc
There are loads of threads on here about house keeping routines - have a look - they usually follow the pattern of spending 30 mins in one room per day.
Remember to build free time for yourself in to your routines if at all possible; because if you don't, no one else will!
Good luck!
Btw - the guest thing - it becomes a vicious cycle. If you really want to motivate yourself then set a date and invite people around in six weeks.
Nothing like the fear of guests coming to get me off the sofa!!