Daisy has a strawberry birthmark on her left shoulder blade and it started off very similar to Poppy's. I didn't notice it when she was first born but we had a newborn shoot done at 13 days and it wasn't until we got the pictures back that I noticed it. I didn't really think anything of it until about 5/6 weeks when it started raising and it's now huge and still getting bigger. My biggest concern was how painful it looks but when I spoke to my HV he said that they can grow for 12 months and are generally gone by the time the child starts school although how they go is beyond me, but that also they don't cause any pain. I've attached some pictures of it at different stages just so you can see when it looks like now compared to how it looked to start off with.
13 days (tiny red mark in her shoulder)
https://i301.photobucket.com/albums/nn45/KayleighJayne02/KMackenzie-ONLINE-6.jpg
This was 6 weeks old
https://i301.photobucket.com/albums/nn45/KayleighJayne02/Mobile%20Uploads/image_11.jpeg
And this is how it looks now
https://i301.photobucket.com/albums/nn45/KayleighJayne02/image_173.jpeg
I also spoke to a HV at a drop in clinic when I went to get her weighed about it and she said if I wanted I could take her to a GP for them to keep an eye on it but that generally nothing will be done until after 12/18 months of age because of the fact they tend to disappear. From a vain point of view I'm lucky it is on her back because you can't see it but it does stick out and you can see the lump as well as feel it through her clothes.
My eldests was like this with the swelling underneath, though a bit smaller, hers was between her eye and ear.
It's bizarre how they go, when she was 2 she started getting skin coloured lined through it, breaking it up. Within a week it was gone- the birthmark, swelling the lot, no evidence of it ever being there!