I'd like to arrange a day out to London with DD8 that wouldn't really suit my rather rambunctious DS5 (early start, long journey, quiet exhibition...), and DS5 would have a special day with DH in our local city that is more suited to his energy levels.
Going to London for a day out would really be a one-off, at least for the foreseeable future. It's a long way for us (over 3 hours) and I can't imagine taking DS there on his own for a day out for at least another few years (until he's DD's age really).
So my question is, would it be unreasonable to take DD8 on this day out when I have no intention of replicating it for DS5 for at least a few years?