Translation:The small foxes run from the fence to the trees.
For the English translation there won't be a difference. The first sentence is focusing on the action (putting emphasis on elfutnak) and the second sentence puts focus on who is running (emphasis on rókák).
Also notice that kerítés doesn't contain an 'h'. The Hungarian letter 's' already makes an English 'sh' sound.
It can be either in this case. Usually you'll tend to use the shorter kis in front of a noun, unless you want to put extra emphasis on the smallness or the next word starts with a sibilant. ("Kicsi szék" is easier to pronounce than "kis szék"). But it doesn't matter a lot what you choose.