Translation:Yes, these shoes are a little small.
Ser is conjugated according to the subject/object. Zapatos is conjugated as son (they are) because zapatos is plural, it's not singular, there's more than one. So it would be estos zapatos son, these shoes are.
If it was singular ese zapato es, that shoe is, it would be the singular form of ser which is es (because es is the ser conjugation for she/he/it/you):
Ese zapato es... That shoe is... (or according to the ser conjugation - it is)
Estos zapatos son... Those shoes are... (or according to the ser conjugation - they are)
You'd never get yo soy, tú eres, nosotros somos for objects because they refer to subjects not objects: I, you, we.
More here: http://www.spanishdict.com/conjugate/ser