The reason most of us need arch support is to deal with flat feet or with collapsed arches. Most babies may look like they have flat feet, but it is important to realize that most babies have seemingly flat feet. The operative word here is seeming.
This is perfectly normal for most children younger than sixteen months. Please don’t rush to fix it with shoes with arch support. However, if, after this and after an official diagnosis, your child needs arch support, you can get this as insoles to add or remove to the child’s regular shoes.