Field mouse spotted in my garden where I keep ducks - kill or ignore?

Two of them spotted tonight nibbling on some spilled cracked corn. Ducks in their cages.

My question is, does the disease risk posed justify getting rid of these mice?
While they're cute, I am unaware of how severe the risks of:
1. Serious multiplication
2. Will they attract raccoons to come and eat them
3. Disease via droppings risk?
otherwise, hell I'd like to keep them as pets but I'm unaware of how severe the risk is. My garden is rather closed up (within a city + neighbors)