Hello
We recently published a review that summarises the availble evidence on sex and malnutrition in children. This does confirm that, in most contexts, malnutrition is higher in males than females. Incidentally, this is also the case for U5DR.
https://gh.bmj.com/content/5/12/e004030
In the paper we speculate a little about possible reasons for this sex difference. Myself, I suspect that, as mentioned above, the time out of the house, away from the kitchen, may be important. However, more research is definetely needed to understand the risk factors better. There is another paper coming out soon where we explore in more detail the possible mechanisms involved.