Well, it depends on the age of the boy. If it's a small child, it's usually genetics that make the child small or skinny, so there really isn't anything you can do except make sure the boy is getting all the nutrients his body needs and just wait for a growth spurt. If you're talking about a preteen or teenager then there are protein shakes and protein bars you can get from the health store. Peanut Butter has a lot of protein, so PB Sandwiches would be good for a boy of any age.
You're fatten
If you're worried that he's too thin, which is probably why you asked, it's nothing to worry about. If he's losing significant amounts of weight, take him to a doctor. But there's probably no need to "fatten him up".
The noun form for the verb to fatten is the gerund, fattening.
A verb for fat is fatten. As in "to fatten something". Fattened and fattening can also be used as verbs.
no
no you can not because it is a lquid and lquids cant fatten people up
They aren't. Harmonies don't make cattle fatter nor fatten them up.
There are a number of ways to fatten up a turkey. The best way is to feed it and keep it happy.
Capon
marshmellows
No. Water has no calories.
Feed it high protein feed.