About the only way you could put beans out of the reach of bunnies - but within the reach of pre-schoolers - would be to fence in the whole garden.

Provided that the problem is rabbits (not deer) a 36" chicken wire fence would keep them out. Be sure that the chicken wire has no gaps at ground level... I hill up the soil about 4" over the bottom wire. For a gate, you don't need anything fancy, unless you feel so inclined... just a removable frame, covered with chicken wire, tied between two posts. I do this on one of my small plots, and secure the gate with a couple pieces of aluminum wire used as twist ties.

Rabbits are a big problem in my area too; I've seen 4-5 in my back yard at one time. Because of that, all of my gardens are surrounded by chicken wire (and high fencing to keep out the deer). Without fencing, gardening would be a pointless effort... I'd be feeding the wild life, not my family.