Note that the Virginia tax deduction is per account, not per tax payer or per beneficiary. If you have three kids, each with a separate account (meaning three accounts total) and you contributed $4,000 per account, you can deduct up to $12,000 from your Virginia taxes in a single year. If you were to contribute $5,000 per account instead for a total of $15,000 you could still deduct only $12,000 but the excess ($3,000) could be carried over and deducted in the following tax year.
More details with a few examples are at https://www.virginia529.com/learn/tax-advantaged/
