Apron dress Cloak Hood Kaftan Linen tunic / dress Pants Wool kirtle / dress
Can be a bit of a nightmare. The more effort you put into the outfit, the shorter the time until it's too small. At least that's how it feels sometimes. I have been making kirtles, tunics and assorted stuff for my son since he was about 15 months old. He is 9 years old now.
The good news is that it's fairly easy to make a pattern for a toddler or small children. As long as you remember to make the neck opening big enough and the armholes wide enough. Despite what it looks like when you try to dress them, small children don't bend as well as adults. No tight armholes and upper sleeves or too tight fitting upper bodices without buttons.
Use natural fibers. Pure wool or wool with a little polyester or other natural fibers is fine. Linen or linen with viscose rather than pure cotton. About 50% cotton and 50% linen was fairly well known from the 14thC. One material was used for warp, one for weft. Silk of any kind as long as it's pure silk and not synthetic. Fur rather than synthetic. Second and third hand fur is an alternative to new fur. The clothes looks better with the correct materials and small children don't need much fabric anyway.

Wool, linen and silk are less flameable than most fabrics and safer around campfires. Wool will keep your child warm when sitting still and breathes when they move. It's even warm when wet.

Linen is cool when it's hot and the fabric breathes. And is much more comfortable in hot weather than cotton. Cotton is not a good substitute. It moves differently ,absorbs humidity and clings where linen tends to breathe.

Silk is silk. Cool to the touch, doesn't chafe and is even comfortable in cold weather. Just remember that silk is not a full garment material for anybody but royalty and the very rich until the renaissance. And for most people it' was still a luxury. Use silk for lining around necks,in hoods or as decorative trim.

With a few exceptions, most extant garments covering viking to high medieval, have little trim or embroidery. Some very nice finishing touches and simple decorations is not unusual though . If you do not portray somebody rich and wealthy, you should keep it simple.
If you do trim; consider card woven trim, metallic trim that looks like trim from paintings or manuscripts of the time you make the garment for,or some simple embroidery.
Bands of silk as decorations on garments is fairly well documented.
This is a question of taste,patience and if you do re-enactment or sca /ren-faires.
Personally I prefer hand sewing. Partly because there are a lot of short seams to fiddle with. Partly because the garment moves very differently when hand sewn. And it looks better. And I like hand sewing wool for some reason. And of course it's historically correct.
I would recommend hand finishing the garment if you prefer machine sewing. It's the only way to get those little historically correct finishes.
On the bright side, it's not that hard to hide machine seams. Either by doing a chain stitch to cover visible machine seams around the hem, neck, end of sleeves or hand stitching on trim or silk in the same areas.
Trim is usually faster to hand stitch unto garments than machine sewing .
Extant sewing thread falls into 3 categories ; wool, flax / linen or silk.
1) Wool ;
A large number of extant garments were sewn with wool thread. Wool thread can be a nightmare while sewing. Until you get the hang of it that is. On the bright side, when you have finished sewing, you have a very elastic seam that works with the wool. After a wash or two, the seams will have "joined" the fabric. I find that 30-40 cm is the optimal length of the wool thread. Short enough for comfort, long enough to get some sewing done. There is also the reduced risk of fraying. Pull gently. And use a tapestry needle with a big enough eye.
I recommend wool thread for fabric that has a lot of stretch, thin wool and wool that frays.
2) Linen ;
There are extant wool garments with traces of flax where the seams have disintegrated. Linen thread is strong and doesn't break easily when sewing. The seam isn't very strong though and linen seams often needs repair and don't stretch well. Wax the thread ! Use beeswax or candles if you can't find beeswax anywhere. It makes it easier to sew and makes the thread less likely to fray.
LInen thread is excellent for linen fabrics and thick wool that doesn't stretch much or when you need a lot of force when sewing the seams. Also for thicker silks.
3) Silk ;
Thin to strong thread that doesn't stretch much. Can be used when sewing thin wool. Great for finishing touches like buttonholes. And of course, perfect for sewing silk. And can now be used for machine sewing too.
*Archaeological Sewing, By Heather Rose Jones
*Sewing Stitches Used in Medieval Clothing, Compilied by Jennifer L. Carlson (Bronze age to early 17thC)
*Some clothing of the middle ages, Historical clothing from Archeological finds. Compiled by I. Marc Carlson