As I watched, the sun broke weakly through, brightened the rich red of the fawns, and kindled their white spots. :
Please answe these questions I have.
[1a] What kind of flame does kindled imply?
[1b] How does this verb suit the purpose of the sentence?
[1c] Would the sentence be strengthened or weakened by changing the sun broke weakly through to the sun burst through?
[1d] Explain the effect this change would have on the use of the verb kindled?
Without knowing the original passage and the larger work, it can be difficult to parse the meaning of a sentence like the one in question. However, we can make a few guesses by looking closely at the words and their definitions and relationship to each other.
To "kindle" means to start burning, or to stir up. So the flame in question is "stirring up" the white spots on the fawns, as if causing those white spots to catch on fire. "Kindling a fire" means starting a small fire by rubbing sticks together or using a small flame (like a lighter) to ignite the "kindling," which are small branches. Eventually, the small flames you've kindled grow into a larger fire.
Again, it's difficult to guess the purpose of this sentence without knowing what information comes before and after. However, the language does personify the sun as weak, and the fact that the sun breaks weakly through the clouds emphasizes that the sun is struggling to shine on the young deer below, to bring out their fire-like beauty.
Furthermore, the sun's weakness parallel's the fact that the fawns are young and, we can assume, relatively weak. So changing "broke weakly" to "burst" would destroy that similarity, and give the sentence a much more triumphant tone, rather than the tone of understated struggle that's currently present. Again, whether that change would strengthen or weaken the sentence depends on the context (what comes before and after).
Finally, if "broke weakly" were changed to "burst", the sun's flame would clearly be a very big, powerful flame, rather than the weak but fighting flame that is currently implied. Such a change would alter the dynamics of the images here, and alter the tone, though for better or worse is for you to decide. Consider which of the two versions is more fitting for the larger piece in question--which is more in keeping with the emotions, themes, and imagery of the rest of the paragraph, and of the work as a whole?