Posted: 15/04/2015 at 14:43
Decking provides an ideal home for rats - I wouldn't have it in my garden. Get professionals in to get rid of them and get them to come back on a regular basis until you and they are sure the problem is dealt with.
Clean the playhouse and toys with Dettol solution or similar - don't leave them out at night. Teach grandson to wash his hands properly after playing in the garden and not to put his fingers in his mouth, eyes etc. make sure wounds have a plaster on them.
Make sure guinea pig food etc is in rat proof containers.
And then, don't worry too much