We were at Disney about 2 weeks ago and for 2 adults (presumably it shouldn't be too much different for you and your kiddo) with 3 sets of FPs (our advanced and two additional sets based on bands we got from relatives) to manage, it didn't prove to be too difficult honestly. The first day may have been a little rough since I had to get used to locating kiosks and in general, navigating the process of remembering to take pictures and which pictures corresponded to which set of bands. After the first day, and once you find a system that works for you - fortunately, the other bands we had were different colors so wasn't hard to remember which set was which, and then remembering the first picture taken is always for the "red" bands and second for the "blue" - it became a breeze and we actually manage to get Tier 1s like Soarin and Test Track more than once on a couple occasions AND after we hopped to Epcot in the afternoon (likewise with the Tier 1s at HS), but we went in with expectations in check, so it was a nice surprise. MK worked the best given the abundance of availability. Quite frankly, I don't think we waited more than 10 minutes for anything, including both FPs and standby, so it worked wonderfully.
Back to the original question, it wasn't difficult to manage more than two sets at all, again, once you find a system that works well. I actually found myself remembering my SDFPs more so than my advanced ones lol. And in the rare instances where we scanned the wrong band, CMs don't even bat an eye
Hope that helps.