Hello! Welcome!
Littles make it super hard to concentrate on writing, don't they? I have one that is almost 4, and then two that are 14 months, so I feel your struggle. The gold standard of goals is just butt-in-chair-time, really. Right now just finding a way to carve out time, whether it's an hour you can magic up to dedicate to trying to make words, or three fifteen minute blocks that you trade for bribes of goldfish and apple juice (shamelessly) if you can conquer getting the discipline to write even a little bit, every day, you're light years ahead of where you would be without that discipline. I mean, today is Day 258 of 2017. If I'd managed to sit down and write even 100 words every day since January that would be 25,800 words that I don't have now because I didn't manage to write every day for most of them.
But what's a realistic goal for you? 100 words a day? 200? 500? Aim for something manageable (think doable, not easy) and reward yourself with that feeling of awesome productivity when you get a chance to blow past it. In theory then you can multiply that daily word goal and get a weekly target number and a monthly target number so if you have days when you don't write anything (or don't write enough) you know how much you owe the word bank to be on target for your personal deadline. Or you get halfway through the month and realize how far behind you are and just how far you have to step up your game to meet your goals...
But just getting in the habit of writing every day is a good place to start. And a hard one. It's one I still trying to master.
Aside from that I've found that the community here is good for positive peer pressure. There are several active threads for monthly writing goals, and sometimes the accountability of having to show up and post "today the page won" can be motivation enough to write something instead of nothing.