Is there a limit in the population size?
The population limit is around 90 villagers.

I always run out of berries before I can get enough tech points to increase my harvest level?
Try to put more people at the research table. Also you don't need to always have someone at the berry bush. If there's enough food in your bin (like 150 or so ... even 100 is good for early on in the game), allow that farmer to do some research. Then once your food dips below a certain point, put that farmer back on the berry bush. Remember also that children can spot mushrooms around the village and help increase the food level.

At what age can kids start working and breeding?
Working at 14 and breeding at 18.

How do you build buildings new huts?
Just drag a villager on the construction site (foundations) and he will start constructing. It may take a few tries to get the villager started.

How do I know where to start construction?
Drag the villagers around (hold the villager and don't let go) and they will tell you what they see.

How do you accumulate tech points?
Drag a villager to the research table (center of the village) and they will initiate research and start gaining points. You can also check the preferred skill box for research so that they prefer that activity over the others!

What can children do?
Children can spot mushrooms around the village. But act quickly, because mushrooms wilt rapidly in the sun.

Puzzle 6:
Here the lagoon must be completed. Then you drop a Master Farmer into the lagoon, and he will begin hunting a strange fish. This fish is only found in the lagoon, so don't even try the ocean, LOL! Level 3 of Harvesting is required for him to be able to find it. The pop up (Celebration time) about the fish will not appear until the farmer has placed the fish in the food bin.

Puzzle 11:
The temple is puzzle 11. The ruins found in the lower right will be restored as the temple. You must have completed level 3 of construction. Simple drag a villager (I use a master builder, though other occupations will help;) drop the village in the pile of ruins, and for their action it should say restoring the temple. If they walk away, keep dragging them back. You can also drag other villagers to the ruins and drop them there. This take quite a while to complete. Please be patient!

Puzzle 15:
As for the Puzzle 15, the buried treasure...to avoid spoiling it for those who want to find it on their own... Your tribe MUST have all 3 levels in Construction and Science. Here's a hint on finding the treasure...drop a master builder (as the treasure can ONLY be found by a master builder) south of the food bin in line with the temple...but I am not saying where on the temple. Drop him/her in the sandy area south of the food bin in line with the temple. Patience, as it takes them a while to find it.