Both still too early for this kind of things... XD
I don't know about you but.. its too early for me atleast
Well that said it's pretty adorable of them making kids wishes and promises .. where they will hold dear till they grow up
6 months ain't that long
I won't say anything about the kiss, that is too personal an opinion.
But... they are 10, maturing sure, but at 10 years old, six months is a significant percentage of their lives.
Most kids only develop a true sense of self around 6, and that is the earliest; from there they truly start to develop who they will be or want to be, and won't stop till their 20s.
So at most, being themselves, they have "truly lived" only for 4 years, 6 months would be more than 10% of the time they "are alive"(in experience terms).
Try to remember how you used to see time when you were around that age, and now, and you will notice how different it is.
Recently I have done that... not like I remember everything XD, but... thinking about it a little, trying to remember the vague feelings I still have from those times... it is... eye-opening in a way.