Wow, there's a lot of ignorance on this thread.
I agree that you have plenty of time OP. You clearly need to find out what happened. There may be grounds for suing. As for 'what for', it depends on the little girl's recovery. Before I switched horses to non litigious work, I was a personal injury lawyer for around 15 years, dealing with all sorts of cases, including a lot of cases involving children. More serious than this sounds (very severe accidents or medical negligence), but the principles are the same.
If, after investigation, there is found to be something lacking in the farm's procedures that caused or contributed to the accident, then, depending on the injury and whether there will be any long term effects, it would be a good idea to get some legal advice.
I've seen lots of children with seemingly innocent injuries end up having years of after care and/or being affected in some detrimental way for the foreseeable.
Some people are being ridiculously inflammatory on here. Of course the OP wants to do the right thing by her child, and, shock horror, that might, at some point in the future, involve taking legal action on her behalf.
I would do the same, in fact, I suspect most of the nay sayers on here would to, if they were in the same position.