I'm sorry to hear that happened to your niece! Not sure what brand you had or where you bought them from, but we buy the 'Merry Art Glow Sticks' 100 in a tube, multi colored w/ connector joints. 1 will make a bracelet or put 2/3 together to make a necklace, the kids love them! We take them out to camp or Disney and give them out to other kids before fireworks (with parents permission, no one has ever turned them down). They are NON-Toxic and I have seen some break on occasion (maybe 1 out of 100), in fact just last week, my 7 yr. old had one leak. She got it on her hands, neck and clothes. She laughed because she 'glowed'! I took her right in and the fluid wiped of with a paper towel. I didn't use water, even on her clothes, it wiped right off. She had no reaction what so ever! I have also seen a few leak at our youth summer camp with the same results. We had to stop some of the kids from breaking them on purpose because they thought it was cool. No reactions, skin irritations or stains. Could have been the brand?...I don't know, but we have been doing this for years and have never had any problems! Now, I will say I wouldn't recommend trying to break them. Check the lable on the ones you buy to be sure they are not poisonous or toxic and you should be fine.