The first chapter of Dragon Quest IV DS starts off in Burland with Ragnar McRyan. Everyone speaks Scottish here so it may be a bit hard to understand at first :) Search around the town for items and talk to the lady in the southwest house. Make note of this Angus guy, then go outside and build up a few levels.
Ragnar has poor agility and lacks the ability to cast spells, but he is unrivaled in power and HP in battle. Use Medical Herbs to heal and once you gain a level or two you are set to move on your adventure.
A cave lies west of Burland. It is small and houses a few meager treasures, but take the north exit and head off to Straithbaile. The kids have been abducted near this village. Search the staircase going down in the far north part of town to meet Angus, so you can return to the lady in Burland and bring her here. After this Angus tells you of a spot the kids played at southeast of town in the forest. Tough enemies are here though so gain a few levels.Try to buy Hardwood Headwear and maybe a stronger weapon, though you will find something very nice soon enough.
The forest to the southeast has a strange well area with voices pulling you towards it. Check the staircase in the northwest first for some Seeds and stuff, then head through the well. Travel southwest as you enter and take the stairs in the far south.
Venture straight east in this B2 level. Eventually you come to a spring with a Healslime nearby. Talk to him, Healie, and let Healie join. Healie and Ragnar make a good duo as Healie can now provide a healing source for Ragnar, while Ragnar continues to mow down enemies. You will also want the treasure across the pond, so return back to that T where you went east, and go all the way north. Now east for some gold and west for a pair of Talaria. Exit out of this place near the beginning.
Try to buy an Iron Armour / Iron Shield at Straithbaile, then rest up. Use the Talaria and you will end of at that tower west of Straithbaile, the one enclosed by water. As you get there, a monster takes the kid away. Follow them down the stairs.
The north path has a worthless treasure so just head south and east for the stairs. West and north in the next area to grab a Scale Shield in the southwest part of the center fortress. Then follow that path for the stairs down. Go northwest in the next room for a Cautery Sword. This makes Ragnar a beast in battle, and it will cast Sizz in battle if used by Ragnar. A Luck Seed is east of here but the stairs down to the south bring you to a spring that restores your HP and MP. With this and the Cautery Sword, you are set to build up levels here if you wish.
Ragnar's Chapter 1 boss Psaro's Pawn lies to the southeast part of that room with the sword and recovery pool. Talk to the soldier to here about the Hero Ragnar needs to find and save. Through those stairs and you will find the kids and two monsters. Go after the Winky first. Hopefully you kill it before it's expression changes otherwise it might blast you with critical hits. Psaro's Pawn has quite a bit of HP, and likes to use Frizz, Sizz, and some powerful physical attacks. Also will breathe low level first at you. Use a Medical Herb on Healie if things get rough, it helps to have him along the whole fight of course. Stay up on healing and if you built up even just a little here, you should be fine.