having completed my excursion i thought i would jot down details as i never actually managed to find a specific piece of advice on where to stop etc.
easyjet from liverpool to ch de g airport @ £120 for 2 adults, 1 infant & 1 baby.
train from c de g to gare du nord on line B @ 7euros x 2 for adults & 5 euros for infant = 19euros (£13) trains every 15 mins at worst, sometimes every 4 minutes. journey time approx 30 minutes
stayed in the ibis la fayette approx 2 minutes walk from the gare du nord train station @ 89 euros per night for a family room (£60)
easy access to the metro from gare du nord.
bought pack of 10 tickets from the machines at the station for 9.6
euros (£6)
huge queue for going up the eifel tower in the lift so walked up the south stairs @ 3 euros each entry fee. this is not recommended, particularly if you are not in peak condition and especially not when you have a 5 yr old with you who requires carrying the last half of the way up and down!
all in all - a good experience but be wary of stairs/escalators up and down with a pram on the metro - slightly awkward!