Are you thinking of little boys beating off? That's not what is happening here.<quoted text>
They are FOUR and SEVEN! I would be on board if they were ten years older, but it's NOT "okay and normal" for children THAT young.
Children that young are not bringing themselves to ejaculation, but they are discovering that some touching feels good.
Parents teach kids that young the difference between bad touch and good touch.That defines who can touch.
It is no different, and probably quite close to teaching a kid that it is okay to poop in the toilet but not in the living room. Both are pleasurable activities that will hapen and part of teh civilizing process is to teach them when and where.