Hi Happyhat,
I spent many years in Morocco & most of my family is there so feel free to ask me questions if you like.
Marrakesh is great as there is lots to visit. I really like Les Jardins de La Majorelle as its very quiet there & away from the madness of Djama Elfan & if youre feeling adventerous you could visit Essaouira which is a great hippy town on the coast about 2 hours away or even the sahara. There are plenty of riads nowadays & prices vary quite a lot.
Dont go in Ramaddan ( i think around sept-oct this year) Feb is a quite a good time to go as it should be starting to get less cold. But March-May is probably the best time of the year as it is warm, but not too hot.
We never bother with carseats unless you're going to hire a car for the whole time you're there (not recommend as driving there is VERY stressful!). Moroccan taxis dont bother with them & most of the touristy places in Marrakesh are not far apart.
Moroccans LOVE kids are they are welcome everywhere and anytime (well, except for nightclubs obviously) But as hoxton said most restaurants dont have any facilities for them ( unless you go to really expensive ones) so take a portable changing mat with you everywhere & bottled water. And nappies & baby things are relatively expensive there so buy everything before you go.
Its quite hard to manouevre prams around as the roads are so uneven & pavement is often non-existant & in the evenings when the souks are really busy so I use a sling quite a bit there.
I ll post again if I think of anything else but let me know if there s anything specific you want to know.