I'm playing vv1 in Hard mode - tech points come slowly and food is scarce. Once all the crops have been harvested and a new set are growing, I want my villagers to return to foraging the berry bush (still has about 80 berries and each villager only brings 2 at a time, so would keep them occupied for a while). But as soon as they have foraged once they just return to watering the crops which, as far as I can see, doesn't make the crops come any faster. No matter how many times I put them onto foraging, they sneak back to watering as soon as my attention is distracted. Then they start getting worried about lack of food. Is there a way to get them more focused on the task in hand - ie picking berries?

I don't think there is a special way, they are stubborn!!
In Hard mode, while you don't have an unlimited source of food, you must "nursing" your villagers a lot!!
(don't forget the mushrooms! )

Trouble is, the child I started the game with is too old for mushrooms and I suspect that breeding another child (even if I can, while the villagers are worried about food) will consume more food than I will gain in mushrooms.

10K tech points to go until fishing... I went for level 2 in science hoping that the increased rate of aquiring tech points would make up for the cost of getting level 2. At the moment I'm not sure that calculation was right - will have to wait and see.

I think you were right.
If you're playing in 2x speed to get the crops faster, don't forget to change for ½ speed before leaving the game. In 2x speed they eat too much!!
I cross my fingers for your tribe!

The cost in level 2 science is well worth it; you'll get to L3 farming faster buying L2 science first. I believe the math regarding the science bonuses is even more forgiving in VV1 and VV2 than it is in VV3.