I don't know specifically what information you are seeking. Are you hoping to tailor two days of sightseeing around a toddler, or just looking for places you can meet their needs for a break?

This thread may be more relevant on the Germany forum, but Germany in general is quite child-friendly. Frankfurt isn't by any means a very exciting or unique German city, but there is a lot to do outside the city if you are planning on doing a driving tour or taking easy train trips. There are a lot of threads about that. As young children we spent a lot of time in the area outside of the city. My parents certainly didn't tailor holidays around us, but there was a lot to do which was still child-friendly.

Otherwise, finding playgrounds, play areas, and child-friendly food won't be much of an issue.

Again, hotel suggestions would be found in the Germany forum for Frankfurt. Suite hotels are not as common as in America, so you would need to decide if you really feel the need to book a suite in a regular hotel to make space for naps, or if you will make do with a regular hotel room, or if you will go the way of a holiday flat rental (not really that applicable for a two day stay)