Celery is a marshland plant with long fibrous stalk. Even though celery allergy is not very common, it is better to stay aware.
Not every child will have an allergy towards the same vegetable. Every child's immune system reacts differently towards different vegetables. The allergic reaction, however, is more or less the same towards any kind of vegetable.
Soy, like peanut belongs to the legume family but a child who has a peanut allergy will not necessarily be allergic against soy and vice versa.