Actually that is not correct. I personally don't drink but lived my entire life in Texas and it is perfectly legal in Texas for a parent to give alcohol to their minor child even in public:
§ 106.04 Consumption of Alcohol by a Minor
(ab) A minor commits an offense if they consume alcohol unless they are in the visible presence of, and have the consent of their adult parent, legal guardian, or spouse.
http://www.gdcada.org/coalitions/aloud/law.htm#10604
Texas
- No one under the age of 21 is allowed to purchase, posses, or consume alcohol.
Possession and consumption of alcohol is legal for minors if under the supervision of a parent, guardian or spouse.
The same is true in New York and a few other states. In some other states a parent can give alcohol to their child is long as it is not in public. In Texas, you can technically take your kid to the bars with you and buy them a beer. That doesn't mean that someone might not call Child Protective Services on the parent but legally it isn't against the law and I've seen it plenty of times at restaurants and drinking establishement. The parent must be there and buy the drink but they can give it to their minor child even if the Chief of Police is sitting at the next barstool.
In Florida, it is against the law to serve alcohol to a minor even if you are the parent.
http://www.youthrights.org/dastatelist.shtml