Save The Children has launched an emergency appeal for £40m to help prevent a famine which threatens millions in East Africa after the worst droughts in 60 years.
Another mother, also called Fatuma, spent a month and a half walking with her four children to reach the camp, in constant fear of attacks by bandits.
She told Save the Children: "I left my husband in Somalia. I do not know if I will see him again. I am worried for him. The war in Somalia is very bad for families. The drought as well is just too much. We cannot cope."
The Dadaab camp was originally built for 90,000 people but the population has risen to 370,000, leading to violence and exploitation among the inhabitants.
Children who arrive unaccompanied are particularly at risk of violence and abuse, with trafficking and the recruitment of youth into armed forces also a problem.
Save the Children tries to trace family members for the lone youngsters, or places them with suitable foster parents from the same clan.
Hassain, 16, travelled alone with his two-year-old sister to reach the camp where the charity has helped him locate his Aunt Abi, with whom he now lives.
The teenager explained: "My father sold everything he had to buy me a seat on a minibus. I strapped my sister, Sareye, to my back and climbed on. It took six days to cross.
"I was very scared the whole way here. I was scared for myself and for Sareye. She is only two years old."
Matt Croucher, Save The Children's regional emergency manager for East Africa, said: "We can stop this tragedy unfolding, but we only have half the money we need. We urgently need to raise the rest so we can save more children's lives."
More than a quarter of children in the worst-hit parts of Kenya are now dangerously malnourished, and in Somalia malnutrition rates have reached 30% in some areas.SOURCE: SKY NEWS