ITV has apologised to Freeview users in Wales because they can no longer receive the station's children's channel.
CiTV now broadcasts an extra five-and-a-half hours on the weekend
The commercial broadcaster has moved its multiplex - or group of channels all broadcast on the same frequency - to increase programming on CiTV.
But that has meant people with Freeview in Wales cannot watch CiTV.
ITV said it would try to return the channel to Wales, and it was still available via satellite and cable.
The change is a result of the station having acquired new capacity for CiTV in order to extend the hours of the channel to 12 hours, seven days a week.
It means that young Freeview users in Wales are missing out on such CiTV series as The Giblet Boys, Planet Sketch, Blips and Horrid Henry.
A spokeswoman for ITV said: "We apologise to those viewers who can no longer access the CiTV channel.
"Like all broadcasters we must make decisions on how best to use the capacity available to us.
"We believe that the extension of the CiTV channel's hours on the weekend via acquisition of this new space (on the SDN multiplex) is the most positive step available to us at this time, both for the future of the channel and the benefit of its wider audience," she added.
However ITV said it would try and acquire capacity to return to Wales if it became available in the future and would resume broadcasting the CITV channel across the UK.
The spokeswoman said the channel was still available in Wales via satellite and cable and would be available via the new Freesat service due to be launched this year.
Freesat, which will allow viewers to receive free-to-air channels through a satellite dish, is a joint venture between the BBC and ITV and will also provide an alternative to BSkyB and cable as a way of receiving digital channels.
The independent communications regulator Ofcom said in a statement: "The DTT multiplex operators have a must-carry obligation to all public service broadcasting [PSB] channels, including all BBC channels as well as CBeebies and CBBC.
"ITV1, Channel 4 and five and various channels run by other broadcasters are not PSB channels and therefore do not have a special place on the DTT multiplex.
"It is up to ITV as the broadcaster in this instance to obtain additional spectrum on the multiplex for CiTV as a channel."