This isn't true. I've seen children in many of the lounges, and they all serve alcohol.
Yes it is not true, United Club members may bring their families, below is directly from website.
Home > Travel information > Airport information > United Club and lounges > Club access
Club accessCustomers ticketed with other Star Alliance® carriers should consult the policy from each member airline or the Star Alliance lounge policy regarding lounge access.
United ClubSM members
United Club members have access to United Club locations and select partner lounges. Access privileges and credentials vary by club type. Refer to the chart below for more details.
Clubs or lounges Access Guests allowedc Credentials required
United Club
US Airways Club
2 or familya United Club card
Valid ID
Star Alliance branded loungesb
and Business Class lounges owned by Star Alliance member airlines 1 United Club card
Boarding pass for travel on a Star Alliance flight departing from the airport in which the lounge is located
a. Family is defined as the member’s spouse and children under the age of 21.
b. The Star Alliance operates branded lounges in London, Los Angeles, Nagoya and Paris.
c. Guest must meet the same Star Alliance itinerary requirements as the member and access the designated lounge with the eligible member.
United Star Alliance Gold members
United Star Alliance Gold members may visit Star Alliance Gold lounges. (Look for the Star Alliance Gold logo at the entrance.)
Access privileges and credentials vary by club type. Refer to the chart below for more details.
Clubs or lounges Access Guests allowedc Credentials required
United Club
US Airways Club
1 Star Alliance Gold card
Boarding pass for travel in conjunction with a Star Alliance international flight
All Other Star Alliance Gold Loungesd
(look for the Star Alliance Gold logo at the entrance) 1 Star Alliance Gold card
Boarding pass for travel on a Star Alliance flight departing from the airport in which the lounge is located
c. Guest must meet the same Star Alliance itinerary requirements as the member and access the designated lounge with the eligible member.
d. At some departing airports, a contract lounge may be available. Invitation to access the lounge will be presented to the customer during check-in.
United Global FirstSM, United BusinessFirst®, United First® and United Business® customers