Hi Eb, I am just back from 5 days in Marrakesh with a 3 year old and a 13 month old. You will be fine. It is very safe, but you will need to watch the narrow streets in the old town round the medina with your little ones - the Marrakeshis love their motorbikes!
We stayed in a riad in the old town and it was lovely, our room was very big, with a lovely 4 poster bed, a separate bed for our DS1, and a travel cot for DS2. It was very calm and relaxing after the madness of the souks.
We went to the souks, once again very safe but watch the bikes, the market sellers will try to charge too much (aka rip you off) but you always have the power to walk away and go somewhere else.
I didn't feel threatened, but it was cool enough to wear jeans a long sleeve shirt so I was reasonably well covered up. It is very touristy though, and lots of people take babies / young children, so you won't stick out.
DS1 was old enough to walk everywhere, and we had DS2 is a Baby Bjorn, but there were lots of people with buggies.
With regards to change facilities, I changed DS2 on my lap in the toilets of restaurants in the main square, and we took sterilising tablets for his bottles.
All in all I would recommend it. The Marrakeshis love children, and you will be safe there.
All the best,