Train strain

I have been trying to sort out transport for myself & my girls for a trip in the school holidays.  I will be travelling alone with them.  I looked into flights and OK yes I am booking late but jeez, 400 odd quid for flights to Glasgow?  Are the seats gold plated?

Righto so am now looking into the train option.  Sleeper would be ideal (although the thought of sleeping in an overpriced cupboard does make me start to hyperventilate, the adventure of it plus not having to entertain my gorgeous girls for 5 hours is appealing).  Despite having a Friends & Family discount card it is still ridiculously high in price.  Mostly because you pay for your tickets (and I only have to pay for myself & Girl 1 as Girl 2 is under 5) and then you have to pay again for the sleeper cupboard berth, which in effect more than doubles the cost.  Ah, because, I am told my the nice Scottish man on the phone, children HAVE to go in the berth's as they might disturb other passengers.  Teenagers, being more responsible (?), can go in the carriage but not children.  In my head I know this makes sense but I still feel aggrieved as I feel I am being penalised for even attempting to travel with kids!

just because they give me a crap eye mask and disposable toothbrush does not make the additional £120 cost worthwhile

OK, so back to the regular train option.  No, it'll be alright, I'll just pack DS/Leapster/colouring/books/snacks (Girl 2 is always hungry) etc etc etc.  Yes this is better £90ish, but what is this? Because I am not paying for a seat for child 2 I cannot reserve her one?  Surely there must be a way to do this?  Have just looked on the rail enquiries website and no, I can't.  Well that's just bloody great.  And they advise

As with any ticket, if seat reservations are available on your chosen service you will be able to reserve your child a seat for the journey. Seat or sleeper berth reservations are not available for accompanying children who are travelling free of charge. If you wish to reserve a seat or sleeper berth for your child under five - or to ensure that they do not need to give up their seat during their journey - a child discounted ticket may be purchased and a reservation made.

You have got to be kidding me. This surely is very unfair.  Obviously I don't want my child to have to stand for this journey and so may have to pay for a 4 year old.  I feel like I am being punished for

a) having children
b) even thinking about inflicting them on the public

My girls are fairly spirited but ultimately very well behaved (although I reserve the right to change my mind after a 5 hour train journey with them with possibly one of them standing!) why is there an assumption that children behave worse than any adult?  I have experienced adults who are much much worse (hog space, eat stinky food, talk loudly on mobiles, put feet on seats & drinking to name a few misdemeanours).  This just does not seem fair.

What do you think, am I being unreasonable?