I have worked a lot with learning difficulties children and adults and some with very challenging behaviour.
I would provide wash facilities with that sterile hand wash and paper towels for a start.
Remove any tools or ladders from the area children and carers are going to be, my bad experiences when people do not put tools out of the way
All animals pose a big risk, especially when they carry weapons, the children may also pose a risk to the animals, kicking, biting and hitting are common and also shouting or screaming can upset or over excite animals.
I am not sure of your set up but, any child visiting would need 1 -1, some maybe 2-1, I have worked 2-1 and its been needed for safety.
Secure area where the child is not going to trap fingers or run onto a road or thorn bushes and maybe introduce just one dog rather than all 3 at once, unless they are fences off and only watch.....now I am sure I will think of a risk assessment but with children and adults with behaviour issues, what can happen will..
Being knocked over
Bitten
Trod on
Squashed
a lovely thing to do though, I worked with a very scary boy who the psychologist suggested we treat like a puppy and it actualy worked, good boy etc and a high quiet voice!!