My God, I am in the same situation just like you. However, I am lucky to have 15-85mm already.
Since you have 18-55mmIS and 50mmF1.8 and your little girl is 1 year and 4 months old, I am guessing you and your wife often take your little girl out, right?
My recommandation to you is to get 15-85mmIS USM for your 60D. It is a great lens for your camara body and you will find yourself a lot happy with your family since you will likely to take them out more.
28mmF1.8USM is a great lens too but it is impractical to use this lens to chase your little girl's movement either indoors or outdoors. You have 50mmF1.8 already and please continue to use it in the house. What you need at your little girl's age is a outdoor lens.
If your wife has problem of your spending too much money then maybe you would consider another great lens for your 60D at a great price. --> Tamron 17-50mm VC B005.
I like your attitude of wanting the best for your family. Please keep on taking pictures of your family and thank God they have you as a good father and a good husband.
If you live in Taichung, then you are welcomed to come to me and I will lend you my lens so you can try them out and see for yourself what lens is best to suit your needs.
EF28mmF1.8 is an excellent choice for every APSC camara and new fathers. I would like to share with you why I did not buy this lens to take pictures of my twn sons. As you can see from my signature, I don't really have wide angle lens but rather I pursue "portrait" lens such as A09 and S50F1.4 and EF85F1.8USM.
I always have this puzzle of wondering why most people claim any focal length longer than 50mm is not suitable for APSC bodies when used indoors. For me, I even find it enjoyable to use EF85mmF1.8 to take quick head shots of my twin sons in the livingrom. Of course, my focus is on the facial expression of my son. 85mm is just right size for me to take that facial expression.
I also have this puzzle of why people do not like to share their lenses. I have only one friend who uses Canon and I feel comfitable to lend him every lens I have so that he could test and compare before he buys any new lens. Does lens has this life limit as at certain shutter count then the lens would die? I mean, after all, my lenses are not expensive compare to L series. I even ask myself if I would still lend him L lens if I had one? Well, I guess I would. My point is if the lens is sitting crying in the anti-moisture box; why not let itout and have someone to take pictures with it and have a great momory?
In the deep place of my heart, I really admire people who spend time and efforts to take pictures of their family members. Just like Loka who invests his own time and money just to make sure his family has the very best they deserve. Loka's family is lucky to have him as a father and a husband.
To me, lens is never a question but rather I do care more about whether or not I could capture the memory of my family especially my parents.