Btw, thank you Malte, for fixing the All Caps on the title of this topic.
I'm only about 5 ft 2. Littlefoot would almost be eye level with me. o_O
With the way he can move his neck around, he could probably look you in the eye pretty easy!

He may be eye-level, but he's bound to have a bit more weight on him than you do!
My question now is, how much do you think Littlefoot weighs? This is a tough question, but I think we can figure it out through ratios and proportions. We are missing a lot of information, so there are a lot of assumptions being made on my numbers
-------------------Beware! Math appears in this section!-------------------------(I'm no math expert. This is just the result of my brainstorming and random logic. I can guarantee there are errors, but it's close enough for our purposes

)
Let's see, an adult apatosaurus weighs about 35 tons, is 15 feet tall, and 80 feet long.
the ratio 15:80 (height:length), assuming that Littlefoot is 5 feet tall, means that he is approximately 26.6 feet long, from head to tail. However, we must remember that the proportions of his body will change as he ages. For example. his neck and tail will grow to be proportionally longer than at his current age (Littlefoot's tail is quite short, proportionally, compared to the tails of his mother and grandparents). It is probably a safe estimate that Littlefoot is approximately 10-14 feet long at this point.
For the purposes of these calculations, I am going to assume that Littlefoot is 5 feet tall and 13 feet long.
If something that is 15 feet tall and 80 feet long weighs 35 tons, what would something that is 5 feet tall and 13 feet long weigh? Tricky question, because the mass isn't equally balanced throughout the total volume of the dinosaur.
Comparing Heights: 5 feet (LF) / 15 feet (Adult) = 0.333 = 33.33% of adult height
Comparing Lengths:13 feet (LF) / 80 feet (Adult) = 0.1625 = 16.25% of adult length
To find the average difference in size (height and length):
0.333 + 0.1625 = 0.4955
0.4955 / 2 = 0.24775 = 24.775%
Littlefoot is therefore about 25% of his average adult size, based on length and height.
The problem is, this doesn't factor in the change in width/girth of the dinosaur. I am assuming it remains the same proportion for the purpose of this.
factoring in girth as well, which I am assuming to be the same average proportion, 24.775%
(0.24775)^3 = 0.0152069105
Littlefoot's size = 1.52% of total adult size
This last step assumes that adult size is proportional to adult weight. Therefore Littlefoot is 1.52% of his adult weight.
Calculating Littlefoot's weight based on his percentage of adult size:
35 tons (adult weight) x 0.015206 (percentage of adult weight) = ~532 lbs
-------------------------------End of Math----------------------------------Therefore Littlefoot weighs approximately 532 lbs.
What do you think, does this seem somewhat reasonable? I know these calculations are not scientific at all, but it's the best I could pull out of my head

Remember too, that if our size estimates are incorrect, this weight will also be incorrect.
If there are any math whizzes around here, challenge me! Does this make any sense?