Fattening children up - ideas needed

[Kiriwawa]

DS is super skinny/underweight/not really growing and has no interest really in food. I can count the times he's said he was hungry in 2012 on one hand.

He likes junk food (chocolate, crisps, chips, sweets, etc) so I could stuff him with those in an attempt to get him to pork up but I'd like to try and give him some high calorie deliciousness that would not be horribly unhealthy.

Anyone got any ideas?

My DS (4) is the same, no interest in food or eating it can be quite frustrating but i've learned to live with it as he's been like this since birth! He's not skinny but slim build although has somehow managed to stay on the 75th percentile since he was born. He eats lots of peanut butter which is very high fat/calorific. I add lots of butter when cooking for him, cream too if poss for example creamy pasta sauce, lots of cheese, full fat milk, home made smoothies made with full cream milk & yoghurt & banana, avocados are great for good, very high fats but my DS won't eat them, maybe yours will?! Oily fish like salmon is high (good) fat too, jacket potato with lots of cheese and butter. Protein such as eggs, roast beef, good quality sausages. Pancakes are good and you could fill with a high calorie filling sweet or savoury. Meals using mince such as lasagne & cottage pie are good as fairly fattening but very nutritious and "bulky" if you see what I mean!
Hope that helps! x