A picture will be better so we can see what you mean. Normally the tail base should be plump and no bones sticking out at all around the hips.
The head up and with tail tip curled up means the dragon is in alert/hunting mode. My dragon does this all the time when I give her food or she's tromping all over her cage.
From what you said, it is possible your dragon was scared by your nephew if they were trying to catch it or banging on the side of the cage etc. It may be a good idea to lock your bedroom door when you are not around to supervise.
When your dragon was eating normally, how much crickets did he eat? How often did you offer food? Are you also providing greens? Dragons from hatching up to 4 months of age should be fed 2-4 times a day insects with salad available all day (even if they dont' touch it). After 4 months 2 feeding of crickets a day with salad available all day is good. Once they reach about 8 months one feeding insects a day and salad all day is good. After 14 months, salad every day, insects a couple times a week, or a small portion with their salad daily (2-4 adult crickets, superworms etc).
Insects should be all they can eat in about 5-10 minutes for babies up to about 8 months.
Another question, are you gut loading your crickets? Feeding them mixed greens, a commercial gut load or similar, at least 24 hours before feeding them to your dragons? If you buy the crickets from the petstore or even mail order, and feed them right away, often those crickets are starving and thus provide little 'meat' to your dragon. It is recommended to gutload 24 hours before feeding the crickets to your dragons, to ensure they are well fed and not just empty shells.
If you normally are feeding alot to your dragons and they still seem skinny nor seem to grow much or gain weight...I would take them in to see a vet and get a fecal done. Parasites can definitely rob the dragon of valuable nutrition even if it seems to be eating alot.
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PHLdyPayne