United a website is clear in terms of what is provided (usually nothing) and as always parents remain responsible for their child's wellbeing. Airlines cannot and should not have to provide hot meals on the off chance that someone may 'need' it.
If they want it they can buy something hot onboard, buy something at the terminal or select another airline or mode of transport that meets their needs. Similarly if your child has allergies (real or fashionable ones) then the onus is on the parents to provide. It is not possible to cater for everyone in the confines of an airliner cabin. As with everything in modern day society it's always someone else's fault, it's never my doing, I was completely helpless etc etc.