Hey there Bob
I touched a bit on this subject in the mens forum last week. I can pretty much start a conversation with anyone.
First task to do…
Most people have some sort of schedule they at least loosely adhere to.
Find out hers, without stalking her of course LOL.
You mention she has a child, maybe she takes the child for a walk everyday or to the playground or something. Maybe she frequents a certain store or pub. I assume you see her here and there when your out now. Once you figure out a way to see her in passing more…
Second task… Practice with your mones a little to find your dosage, You should be doing this while you doing the other tasks I gave.
Third task… Make initial contact
First thing you do is make eye contact with her and smile, Maybe say good morning or afternoon as you slowly pass by wearing your mones. If you see her in passing often, do this a few times before you start a conversation so she has a sense of knowing you a little.
Observe her without being weird looking while your doing it LOL You will notice things about her, If she has her child with her, you can use that to start a conversation. Say "Bonnie little lass/lad how old is he/she ? Now if you read the other post I wrote that I provided a link to above you will no how to continue. Remember Statement then open ended question so she has to respond.
Suppose she shops at a certain store alot. First be sure you know something about the store. If she’s holding a bag or something from that establishment you can use that as a starter. (like the donut shop example I gave in my other post).
Being aware and observing her is what is important. I have a feeling since your walking into lamp posts that your looking but not really seeing. By this I mean get past the Bonnie part and look at what she is doing, holding, wearing anything that can give you a opening to talk to her.
If she happens to drop something, then sure pick it up for her and start to talk but dont stop her and say you dropped something if she didnt. Just so you know men can drop things to LOL Drop something in her path. Not your kilt, something your holding 
You have a advantage really to, other then the mones , You kinda know her sister and you live near each other so you can use those things in conversation to give comfort and familiarity. It helps to start to establish a connection. Dont open with them but you can work them in by saying. "I think I know your sister from school Whats her name ? " or "You live near me I think, How do you like that new lamp post they installed ? " That one is stupid but you get my point. Find a common link.
Your gonna probably get some PUA advice in here to. That stands for pick up artist. There tips on how to get women. Anyways some of the tips are useful but there mostly for guys looking for a quick ummmm… I think they call it “tup” in Scotland. Could be wrong… but anyways your looking for more then that I assume so while the advice can help don’t over do it. Women can smell a PUA a mile away and this girl doesn’t seem like the type to fall for it. Just be you.
Tisha