This appears to be the leading article on the internet re children and altitude.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1112806/Mentions, among other things,specific risks of altitude to infants under the age of 1 (subacute infantile mountain sickness), and about problems identifying altitude-related issues particularly in children under 5.
Also makes a recommendation re sleeping altitude.
"Until further information suggests otherwise, when trekking in a remote setting a conservative approach would be to sleep no higher than 2000m for children aged under 2 and no higher than 3000m for children aged 2-10 years. High treks are no place for little children."
Here is a critique of the Pollard article, which agrees re sleeping altitude for those 2 and under but that contends that, otherwise, Pollard's recommendations are too conservative. Pollard's response follows.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1113767/
