Littlefoot may very well have just proven his genius by what he said, not stupidity. My second ex does this to me often on World of Warcraft:
“Oh, Michael, I’ll never be able to afford that piece of gear. /Silence.”
Me: Hang on, I’ll send the gold right now.
“Oh, Michael, I’ll never be able to solo that boss. /Silence”
Me: On my way.
“Oh, Michael, I’ll never get this quest done fast enough. /Silence”
Me: Summon me.
It’s called making the person feel guilty and/or obligated. Guilty by having the means and not doing it, and obligated by making caring people feeling a sense of duty to someone in need. Many people do it. It’s a common psychological trick to get people to do what you want. Littlefoot may very well have known Elsie could do it; after all, she did just carry him seconds before he said that which may have given him the idea. Secondly, it is awkward for many to directly ask for favors. Many people request help indirectly through vague and/or emotional statements. After Elsie agreed, he may very well have thought to himself, “It worked!” Children are surprisingly clever and devious sometimes, and Littlefoot has certainly proven wisdom beyond his years. This is my guess as to why he really wasn’t stupid.