Hi there
I think you have some lovely interaction there and you have a good eye for special moments. For me taking photos of people/portraiture is all about interaction: either between the subject and the viewer (through the photographer), which usually means eye contact; or interaction between the subject and the environment. Obviously, there is the odd photo with someone staring "wistfully at the past" or whatever, but those are exceptions, IMO.
Kudos for posting for cc, it is such a great way to learn.
I'll give you my cc on each photo (I'm pretty nitpicky, because that is how I like other people to cc my photos)...
1. I think your subjects are too centred. Use the rule of thirds to achiever stronger images. I know they aren't quite in the middle, but close. Also, there is actually just too much background.
The railway tracks are blown out and it is distracting. It is best to try and achieve perfect results in camera, but for this image, now, I would burn them slightly to make it less obvious.
The railway line is running through the little girl's head. Try avoiding this.
I would have loved to have seen this with a shallower depth of field and a nicer b&w conversion. How did you convert?
I think it would have looked lovely if they held hands, but with little children....
2. This looks like a snapshot to me. The flowers in the front are really distracting, the red are super-saturated (I assume in post-processing) and their faces look a bit blown/overexposed. I think the chain-linked fence could look great in this kind of shot, if you have a particular kind of subject.... someone who is less "suburban" looking, KWIM? Once again I think they are too centred and I wish I could see their feet. It looks like the focus fell on the flowers and not on the couple.
3. I like this one, I think with the right post-processing an a stronger crop it could be a strong image.... Try taking some off the left and the top, to place the two little girls image left top 1/3 and see the difference it makes.... Wish you had a shallower depth of field so that your subjects stood out more. I know you don't want people to play with your images, but my hands are itching with this one.....
4. It is a sweet sibling moment. Subjects are too centred, IMO and the photo looks a bit soft. What was your shutter speed?
HTH
Anelle