Is the version on sale on both of these online digital distribution is the uncensored or not?
According from what I read the US version is uncensored while the EURO version is censored. So it would depend what region you are buying the game from.
The worst thing about the censored version all they really did was change the sprites for kids to be invisible, the kids are still in your game but invisible! This was apparently done because European games at the time due to legal restrictions could not contain children in them. The good thing you can just change the sprites to the US version and they appear just fine.
According to this post from the No Mutants Allowed forum it does look like it is the censored version. This GOG.com store page mentions this as well. This page I found mentions it as the censored version as well. So it would appear if you are outside the US and buy it on GOG you get the UK Censored Version. You can however download the fix here as the post talks about it and the game will work fine.
The GOG version is definitely uncensored.
On Steam it depends on where you live.
However if something is cencored Steam will notice you about that.
You can see it in the following screenshot (german store, the orange box right under the video says "reduced violence")
Maybe i should advice you to the No Mutants Allowed Forum - unofficial expansion of Fallout 2 (Uncut Patch included)
Here a Link to an Uncut Patch for Fallout 1 (German Fallout-Files Page)