I'm taking my own children first to see if their are any extra precautions I should take.I'll do an updated risk assessment while i'm there but to be honest i'm quite happy so long as we wash hands and use the antibac gel like we always have.
My view is that it is the hand gels that may be the problem, as those did not exist 10 years ago - whereas the e.coli did. When visiting farms you have to remember that they are a working farm and safety precautions must be taken. That includes washing hands thoroughly before consuming any food/drink. I do not feel that washing hands in the gel is the same as washing hands thoroughly in soap and water. While the alc gels are good for cleaning between touching different animals, I do not feel they should replace soap and water.
I have taken children to farms for many years, including 'real' farms, not just petting farms. Have never had any problems with children getting infections from the farm... but then we don't rely on alc gels - we wash our hands at every opportunity, especially before eating any food.