Did not use a pattern, just looked at several pictures and improvised. Used my standard hat pattern and held yarn double throughout.

Round 1: Started with magic loop and ch 2, work 11 dc into magic loop (starting ch 2 counts as 1 dc) and tightened loop. - 12 sts

Round 2: Join to top of ch 2 from previous round with a sl st and ch 2 (counts as 1st dc here and throughout pattern). Work 1 dc into same stitch and 2 dc into each stitch around. - 24 sts

Round 3: Join to ch 2 from previous round with a sl st and ch 2. Work 1 dc into same stitch. * 1 dc in next dc, 2 dc in next dc , repeat from to * around ending with 1 dc in last stitch. - 36 sts.

Round 4: Join to top of ch 2 from previous round with a slip stitch, ch 2. 1 dc in next stitch and in each stitch around. - 36 sts (I always work just one dc into each dc around on round 4, I feel like it gives the hat a nicer rounded look)

Round 5: Normally, on this round I join to top of ch 2 from previous round with a sl st, ch 2 and work 1 dc into same stitch. Then * 1 dc in each of the next 2 sts, 2 dc in next stitch * around which would increase to 48 sts.
However, for this size (6 months) I only increased to 46 sts, so I believe I worked it as * 1 dc in each of the next 3 sts, 2 dc in next stitch * around. (This would typically be how I would work round 6 if I were making a bigger hat and making it 60 sts around. Hope that makes sense. :/ )

Rounds 6-8: Begin the same way by joining to top of ch 2 from previous round with a sl st, but just work one dc into each st around.

Rounds 9-11: Turned my work instead of joining rounds as loop stitch will show up on the right side of the work. Worked sc around the back side of hat and loop stitch on front and sides of hat. I wasn’t familiar with the loop stitch, but found a video on YouTube that showed how to do it.
If I make more of these in the future, I would increase a few stitches on round 10 as switching from dc to sc tightens the hat up a bit.

For the pigtails: Used a small notebook and wound the yarn around it 75 times, tied off at the top, cut the bottom loops and attached to the side of hat on round 3. Tied an extra string around pigtail in two places and trimmed the ends, repeat for the other side. Tied a ribbon on each pigtail.