Mr Lamb said he had written to TV channel bosses "demanding action".
In a Pink News article, he compared the approach to showing same-sex couples to "the treatment of mixed-race couples a generation ago".
Mr Lamb is up against Tim Farron in the contest to replace Nick Clegg as Lib Dem leader.
Asked by Pink News whether he wanted to see say gay characters in shows like children's TV favourite Peppa Pig, Mr Lamb, the former care minister, said: "If you impose arbitrary limits, you're saying that actually at heart, it's not equitable.
"It should absolutely not be out of bounds, which it appears to be at the moment."
The Lib Dems are electing a new leader as the party tries to pick up the pieces from its disastrous election performance, when it was reduced from 57 to eight MPs in Parliament.
In the interview, Mr Lamb also said the way the Lib Dems characterised opponents during the election campaign was "a bit insulting".
During the campaign, Mr Clegg said his party would "give the Tories a heart and Labour a brain" in a future coalition government.
Asked whether this was presumptuous, Mr Lamb said: "I think you're right - I think it's actually a bit insulting to tell the people that your main party doesn't have a brain or doesn't have a heart. That is like an insult to you, isn't it?"
He added: "I would prefer to get back to telling people what we're about, what motivates us, what drives us through those darkest November, wet, rainy nights, when we're still delivering leaflets and knocking on doors or whatever it might be.
"Are we either slightly deranged or is the purpose something that we really believe in, that's worth fighting for? And that's what I think we could get across."
Mr Farron, meanwhile, has urged closer links between the leadership and activists.
He told a hustings in London that, if he became leader, he would move his office in the House of Commons into the Liberal Democrat party's headquarters to ensure the voices of members were heard at the top of the party.
Speaking on Tuesday, Mr Farron suggested the leadership had become too "distant" from the views of party members and he would seek to reconnect those at the top of the party with its grass roots.
Liberal Democrat leadership contender Norman Lamb has called for more gay characters to feature in children's television programmes.