Great chapter! I loved how they went for a walk and then got caught in the rain. :) I loved the "one rule" Snape gave Harry. I feel that a forboding event will come up soon, just like the rain caught the children by surprise and drenched them, the dark clouds first catching them by surprise, some accident mischief may catch them as well. I love the sibling friendliness and a little rivalry (with the shirt and sticking out tounges). The bed-time story time was too cute! I loved how Harry asked Snape what his bedtime was. LOL! I like how awkward Harry is, I just can't wait until he messes up big time (or a lot of little times, it's bound to happen, tehe). He's being so good so far, I'm a little surprised that Snape is giving him so much freedom actually. But i guess Snape figures that his children are well versed enough not to go along with any ideas Harry has, and that Harry will just follow their examples.
Now for some constructive bits. :) One thing I noticed is that the writing seems a little too plotted out. All of the children's actions are dictated carefully and it is detracting from the reading experience to have everything spelt out so scriptedly. Try to allow a little more freedom, there are a lot of children, but mentioning them all by name and saying everything they do is too much, I tend to forget WHO the children are when I'm reading and when i think of them all I remember as I read is "Snape's younger daughter" or "one of the smaller Snape boys". Try experimenting by describing them differently, once the reader knows who is in the scene, you can use descriptions to name the children and not just their names. you do use hair color a little bit, descriptions of relation to another child like "Oliver's little sister" (be careful with that one, use it sparingly) but I think it's more about the way you label them first that's making the layout of writing seem too careful.Try using dialouge to accompany the actions like so, "What do you mean?" Carlotta asked as she swung around on the swing. It masks it a little while keeping the action fluid.
Try not to list all the children when they do things together. If Carlotta, Harry, Robin, Oliver, ect are all running in the rain, say that "Harry ran with Snape's children back to the house." Don't overdo the positioning descriptions, in the running scene you listed who was around Harry, and who Harry was following. Don't be afraid to call them "Snape's children", don't be afraid to just say "Harry followed them" or "Harry followed his entorage" or something like that or just focus on Harry rather than the children. "Harry ran through the rain, his shoes splashed through puddles" is just fine. A lot of the time when someone is in a different (but non-life-threatening) situation they tend to notice things around THEM more than other people, like in the rain scene, for example, maybe the feeling of the rain on his jumper, the way his breathing was as he ran, the rain drops obscuring his vision through his glasses and stumbling as he ran because he was blind.
Try to keep this in Harry's point of view. You tend to have a bit of an omnipresent view slipping in especially when describing what the other children are doing. (Also one thing that slipped through to me was how Harry identified "scalp braiding" as the braids that the girls had, that seemed too out of character for Harry to know about it without some back explanation. For example, does he know it because Parvarti and Lavender used to do it in the common room? Did a girl in his primary school used to wear it? Harry seemed to be very familiar with it, expecting it to hurt. Be careful because such things are a little too much girl-author things coming through. I know because I do that too, like having Harry scrub the house on his own accord in the summer! lol.)
Try to make this more organic, we are viewing everything through Harry's eyes and while you do a fantastic job of being aware of Harry and what he's feeling and seeing, you tend to focus too much to decisive actions. Try to make small actions come across that way in writing. Try to add more organic descriptions- I know that that is an odd way of saying it, but I think that there need to be more smells and feelings of fabric, breezes and house smells. We all want to be more in the present, as if we were Harry and experiencing all of this.
Great job on the chapter and I can't wait to read more! Thank you for posting it! :)