I actually want to answer this.
When it's a 9-12 year old boy, it's not hard to imagine a situation wherein the boy is experimenting with his sexuality. When it's a ~3 year old toddler it's hard to imagine a situation where he's experimenting with anything rather than being sexually assaulted.
I think a lot of guys did mess around with other boys, and maybe even older boys, before and during puberty. To me it's not that weird to think back on those times fondly. I can't say I was sexually molested at 3, but I doubt I would remember it fondly, if at all.
None of this goes to say that in either case the drawing is morally right or wrong, or "OK" as you call it. It's still just a drawing, and therefore isn't a matter of morality. It's just, as I said, uncomfortable to look at.