Depends on the allergy. If the person is so allergic that they can't be in the same room with other guests eating peanuts or near a kitchen that cooks with peanuts, then no, 'Ohana is not the right restaurant.
Also in the case of a toddler, if you are worried about physical cross-contamination - your child touching chairs and tables, or playing with other children during the games and touching the hands of kids who have been eating peanut sauce, you may want to rethink it. If it's not a contact allergy and is just about ingestion, bring wipes for the kid's hands, etc.
If the allergy is not so severe and the guest only has to worry about not consuming peanuts, then make sure the reservation refers to the allergy and your party will be taken care of.
If it's a case that the peanut-containing items shouldn't be served to one party member, they'll find something else for that party member. If you don't want the items on the table at all, they won't be put there. They might even prepare a substitute. so make sure there is notification on your reservation that you have an allergy in your party.
Also check on the DisABILITIES board for information on contacting Disney Special Diets.