You need to find out exactly how the two accounts are titled. If an account
is an UGMA (Uniform Gifts to Minors Act) account that is in your name
with your mother/father as custodian, then you are entitled to all the money in the account when you become an adult. If the account is indeed a UGMA account,
the bank is supposed to not let the custodian operate the account once the
child becomes an adult, but this does not always happen. There was a
question earlier on money.SE (which I cannot find at this time) in which
the 25-year-old person asking the question claimed that
his father was still buying and selling shares in his UGMA brokerage
account and the IRS was asking why the profits and losses from these
transactions were not being reported on the 25-year-old's tax return.
Money in an UGMA account is not supposed to be used for payment of
household expenses, food, etc. which is the parent's responsibility
during the minority,
but this can well be abused. As to whether money was taken out and
then restored (or possibly not restored, as you seem to suspect),
it is possible
to sue the custodian for improper handling of the UGMA account
and recover the funds, but whether one wants to sue a parent
over what might be a relatively small sum is another matter.
Consider whether most of
what is recovered might go to pay legal fees or other
costs of the recovery process, and will likely ruin
a family relationship.
If the accounts are titled as joint accounts, then either party can
empty the account without informing the other. But doing so would
need information about the account number etc. which you may not have.
For tax purposes, there is also the issue of whose Social Security
Number is listed on the account, yours or your parent's.
See also this answer
for a view of what happens from the other side.