I too have a toddler, and these cats from next door are... messing... on my small tiny 2x3 patch of grass, my paving stones, my doorstep, anywhere and everywhere in my tiny yard.
My back 'area' is only the width of the house and about 10ft long if that, so we do not have much space, every morning there are 4-8 pieces of cat poo.
Council won't help, police won't help, landlord/estate agent won't help. I realise cats are classes as wild animals by some authorities, and domestic pets by others, but it is most fustrating when no one will help... even the neighbour seems powerless beyond keeping them indoors.
Let us know how you get on Dannyboy.