I am too lazy to make a background so here it is...
I wanted to draw something like "A day with Undertaker and kids" so I created a series. This is the first picture of the series that I have drawn. But in the end I made it the last picture just because it's too much work to add in Alan and sometimes Eric in every single picture... XD
And about their age:
Undertaker: ??? <- He's the oldest for sure XD
Grell: 7.5 (in the same grade as Will)
Ronald: 5 (but I think I made Ronald look a bit older than that in most pictures...)
I made that setting mostly based on the second musical. Ronald calls everyone "senpai" so I thought he should be the youngest. Eric just looks like a big senpai so he's like "the big brother next door". And if Will and Grell were "classmates" (based on that OVA with the story of student!Will and Grell), and Alan calls Will "senpai" as well...
Simply it's like: Undertaker >>>> Eric >> Will >= Grell > Alan > Ronald. (William is older than Grell just because I ship WillxGrell XD)
And finally about glasses...
I just thought that it's weird for 5 year-olds to wear glasses.
PS: I just thought that Grell and Alan probably wouldn't get along very well, at least Grell probably would one-sidedly dislike Alan because Alan is cute (referring to that dress part in the musical...)
Ok I can go on and on about this... I should shut up now XD
Part 1: [link]
Part 3: [link]
Part 4: [link]
Done in SAI
Edited in Photoshop
Characters from Kuroshitsuji, by Yana Toboso sensei.