"They receive their religious education right from when they were kids"
Should I use "since" instead of "from"? Should it be "when they are/were kids"?
How can I improve this sentence?
"They receive their religious education right from when they were kids"
Should I use "since" instead of "from"? Should it be "when they are/were kids"?
How can I improve this sentence?
Neither.
You're beginning with "they receive", so it seems like you're making a generalisation rather than speaking about specific people (otherwise it would be "received" - past tense). If that's the case then you can't be referring to a specific starting point, and both "since" and "from when" are for referring to specific time points such as when a specific person was a 'kid'.
If you are wanting to speak generally, about all people in the context, then you could say:
They receive* religious education right from childhood.
*or 'begin'
But, if you are actually talking about some specific people referred to in the wider context, you could say:
They began their religious education when they were kids.