If you want to say that they are pictures of you, you might be better to say "These are pictures of me when I was a kid". To me, "My pictures" suggests they are pictures you own, rather than pictures of you. "these are my childhood pictures" is also a little ambiguous - it could mean pictures of you, or it could mean pictures of your family when you were young. You could say "these are pictures of me in my childhood". Using 'childhood' is a bit more formal than using 'kid'.

'These are my childhood photos/pictures' I use for people I do not know well and I wish to speak in a polite register or be a touch formal. I go back to your original statement 'These are my pictures/photos when I was a kid" when I am speaking to friends, family and I am speaking more casual.