World Vision UK's speaking on Red Hand Day, an international day highlighting the plight of conscripted boys and girls. The charity supports the rehabilitation of child soldiers in Africa and Asia.
Their call comes ahead of a landmark summit in Paris on the issue - one which the Foreign Secretary Boris Johnson has not confirmed he's attending yet.
The summit marks the 10th anniversary of principles agreed by major world nations to end child conscription and support victims.
The charity estimates there are around 250,000 child soldiers in the world. The UN says 59 armed groups in at least 14 countries are kidnapping, murdering, injuring and sexually assaulting kids in warzones.
The UK government recently reported that since the year 2000, 115,000 children have been released from armed groups.
Erica Hall, Senior Policy Adviser at World Vision UK, told Premier: "Our biggest concern at World Vision is that we're not seeing that really joined-up approach with strong, very public commitments to what they're going to do in order to meet those ideas that they say they're striving for."
Speaking about the upcoming conference, Erica added: "What we really hope is that there is a really strong ministerial delegation - ideally led by Boris Johnson.
"They [child soldiers] don't want to be forgotten. Keeping them in all of our prayers so that we know, and they know, that they aren't being left out, and to pray for our government to be trying to do more so that they don't end up being recruited in the first place."
A FCO spokesman said: "The UK Government condemns the use of child soldiers in any country for any reason.
"The UK has provided funding to the office of the UN Special Representative for Children and Armed Conflict in support of the UN 'Children, Not Soldiers' campaign."
Listen to Premier's Aaron James speaking to Erica Hall:
