I swaddled my baby in a swaddling blanket for a short time after he was born, and then moved on to a Halo combination sleep sack and swaddle blanket. He is now nearly 3 months old, and I'm still using it (only at night). For the first few minutes he usually struggles a bit - mostly because he's not interested in going to sleep - but then he falls asleep and seems happy with it; I think it helps him to sleep more soundly but can't be sure. If I don't get to him fast enough in the morning, he usually manages to get one hand out, or sometimes both, and a thumb into his mouth. When should I stop swaddling him? (And after I stop swaddling him, should he still sleep in a sleep sack / wearable blanket? If so, for how long? I know 2-year-olds who are still in a sleep sack...)
Swaddle him as long as he will allow it - probably less than half a year in all, but of course that varies wildly. Then "upgrade" to a sleep sack and use that as long as possible - perhaps until 2 or 3 years old.
We tried swaddling and our son never liked it, so we never actually started. But he moves a lot at night (almost 2yo) and always did, so a blanket wouldn't work for him, especially when it's colder. He's always been in a sleep sack, and shows no dislike yet. (update: at nearly 22 months he suddenly disliked the sack and the crib; luckily it was a breeze to upgrade to a bed and blanket. YMMV.)
The idea with swaddling is to keep the limbs softly restrained, because infants can't control their movements well and swaddling helps them because they don't wake themselves up. Once they develop sufficient motor control, this benefit is moot and swaddling is not really needed but perhaps he will still like it (or not!).
The idea with the sleep sack is simpler; it's just to keep him covered so he won't get cold in the night. As with swaddling, he'll grow out of the need eventually. Even if he'd still kick a blanket off, for an older child (past about age one) that is no longer a serious concern as it was for an infant.
Every child is different and enjoys, seeks, and sometimes requires different environments. Some children can calm themselves best when they have deep sensory information from their muscles and joints. Swaddling is a great way to provide the support that they need.
As long as your child is comforted by swaddling the is no age limit for swaddling. But, most children and parents find that swaddling is not practical as a child's mobility increases and the urge to stand and move about creates a stressful or unsafe response. Follow your child's lead and make the transition when both of you feel ready.
When swaddling is no longer practical, tucking the covers under the mattress tightly, heavy blankets or curling into a ball or scrunching into the corner of the bed provides the same feeling for them. My son preferred tight fitting clothes, heavy boots, and coats for the same reason.
Parents who want to know more about sensory seeking behaviors can read more at http://www.sensory-processing-disorder.com/sensory-integration-activities.html As stated in this article, deep pressure activities are beneficial for all children and lots of fun as well.
Learning about sensory processing helped me understand and enjoy my son so much more because even though he was very bright, his body processed information differently. I've shared this information with hundreds of parents over the years, and many have benefited as much as I did.
Swaddling is mostly to help children cope with their "Moro Reflex". This is the arm jerking they do, which often wakes them up.
You should allow your child to get their arms out! Sucking their thumb is fine; they need to learn how to self-sooth, especially after waking in the night.
Swaddling can happen for as long as it's helpful to the baby. When it's time to wean from the swaddle, you can try swaddling one arm out/one arm in for a week. And then just swaddle around the torso with both arms out until baby seems ready to be in just a sleep sack.
It is helpful to try changes in a sleep routine for 3 nights. If there is no sign of improvement after 3 nights, then it probably isn't time for that change and you could wait a few more weeks before trying it again.
As for the sleep sacks, one time to stop is during potty training so the toddler can get up at night on their own. There are sleep sacks that are made from a heavy, duvet like material. Some babies who loved to be swaddled like these heavier sleep sacks because of the weight. Of course the temperature of the room should be compatible with the weight of the sleep sack.
Your baby will let you know. Each of my four started to struggle in the swaddle, wanting more freedom. Unfortunately, they still needed the swaddle to help them sleep. Swaddling does help with the startle reflex and with the womb effect. Thankfully we used the magic sleepsuit when we could no longer swaddle and all my babies slept great because it helped keep them calm and prevented the startle from waking them. Good luck,
One of ours loved being swaddled and only slept really soundly when she was swaddled. We stopped doing it around 6 months but even there, she was happiest with the blanket on her cot tucked very tightly round the mattress. Even now she likes a full cover.
Our other two always wanted a bit more movement so were happy in the sleep sack things, and they both like to have at least one leg out of the covers (at 5 and 11 now)
We have had good luck swaddling our boy from the arm-pits down. We did a full swaddle until probably about 2 months but then he seemed very keen on having his arms mobile. I imagine it may work because he still feels secure (from the chest down), but has the ability to move his arms. He is now 6 months old and we still swaddle him this way. Since he rolls over now, he actually prefers to sleep on his side, sucking his thumb. This would not be possible with a full swaddle.