Congratulations on your new purse!!
How tall are you? The mm looks nice on you but if you're going to put your kids things in it maybe the gm would be good? I had this same dilemma mm vs gm. I bought the DA rose ballerine in the gm (I have a 2yr old and a 1 month old) and i liked it but I thought maybe it's too big since I'm very petite (4'11). I went back yesterday to exchange for the mm and the two SAs who were helping me and another woman who was shopping in the store convinced me to keep the gm, especially since I plan on using it to carry my kids things also. Im happy with the gm now...my sister on the other hand has a DA in mm and its big enough for her. Her kids are 2 and 4 so she doesn't have to pack a lot for them.
Whichever one you pick will be great. It's such a beautiful bag [emoji4] it's a little more high maintenance than the other two canvases but it still is very usable. I have a totally pm that I got in 2008 when it was first released and it has held up really well through the years. I used to use it every day (now not so much since I carry a lot of things) and it hasn't shown too much wear.