from a science point of view at primary (up to yr 4) is fine.
Surely for the relationship/moral stuff, families can educate until middle school age.
I agree with ilovesprouts why can't we let kids be kids until they are a bit older.
For instance, last night, me and ds were discussing how dd was born (EMCS) and he said that he was born through my bum! I said if course he wasn't and said how he was born and he said "oh yeah - I forgot). That was that. He went to ask how on earth he fitted through my 'twinkle'. I explained how the muscles and ligaments stretch to let the baby's head through and then everything shrinks back to normal when the baby's born. He was satisifed with my full and honest answer.
In their Mika CD it talks about Billy Brown being in love with another man. DD (then 8)said that was silly because men can't love another man. I said that actually they could and that sometimes women loved other women. She was happy with that.
I have a DK book recommended by a friend with older boys and it gives questions kids might ask and then the reply you could give for each age group. It's really good and uses appropriate language for each age.
However, there are certain bits that can quite easily be left out until yr 5/6 and beyond and I don't see the need for lower primary to have diagrams of people having sex (sex in differnt positions in the Lincolnshire video).
They grow up soon enough. I had the yr 5 periods talk and then science-type sex ed at secondary school. I didn't have a teenage pregnancy just because I didn't get taught sex ed at primary school.
I think teenage pregnancies are more to with society rather than the amount of sex ed kids get taught.