Healthy ways to help weight gain

[libertyboy]

My 10 year old son is very thin. He has always been slim but I've really noticed this year that his bones are poking out and you can see his ribs.
I put it down to a growth spurt but his weight hasn't changed since January (only 4 stone 6lbs). Doctors agree he's under weight but otherwise healthy.
He has cereal and fruit in the morning, packed lunch (sandwich, crisps, fruit, juice and a penguin), toast, crisps and free reign on the fruit bowl when he gets home and a home cooked family meal for dinner and then a treat. Twice a week he eats McDonald's with his grandma after swimming practice.
I've encouraged him to drink more whole milk and have been putting butter on his veg etc. He's always hungry but his weight stays the same.
Any calorific hacks to bulk up his meals out there without upping the junk food?
I'll add that he also wants to put on weight but uses it a an excuse to eat crap!

My daughter is the same but has a poor appetite. Doctor recommended adding butter and cream to mash potatoe, full fat milk. Adding cheese, cream and butter wherever possible! We also got ground flax seed which is very high in calories and is nice when added to cereals or in smoothies.

Nuts as snacks and peanut/other nut butters on toast. Ice cream.

Protein and fat.
Eggs in any which way he will take them.
Chicken drumsticks
Cubes of cheese
Yoghurt
Nuts
Oily fish
Avacado
Peanut butter

Will he have a snack mid morning? Can you get protein and fat into him after school rather than carbs carbs and carbs?

cream cheese (on a bagel for snack?)
Greek yoghurt
smoothies with Greek yog, milk, banana, oats

After been diagnosed as anorexic my DD was given a prescription for Fortisip drinks, a small bottle of thick shake in a variety of flavours. She use to have one mid morning and mid afternoon at school, and in conjunction with all the other things posters have said about diet, they worked well to help gain vital weight. Perhaps ask your GP for some. Otherwise 3 meals a day, and 2/3 snacks plus puddings!! It's hard work!

How is he now @libertyboy? Is he gaining? Is he growing any taller? My DS is currently skin and bone but is growing like a weed. I'm giving him lots of homemade milkshakes