Puppy was fast, but tended to make it difficult to find useful info. I couldn't get it to install to my hard drive. I tried Lubuntu, and before some updates it was slow to boot up (getting applications going), but once it was going, it was a juggernaut on old hardware. Puppy was slow to boot, and pretty fast, but I preferred Xubuntu. Puppy would definitely be a good choice for children if you could get it to not run in root all the time.