The kids niche is hyper competitive. My best recommendation, is make content that's got a unique angle on something. Something different from what's out there already, and there's a lot out there already. Then promote those videos. Adwords is the best. Don't choose and set a specific amount like $200, bang and stop. Think of it as an ongoing marketing campaign. You can allocate say $10 for every new video, or $10-$20 across all your videos per day. You can allocate both. You can also do $10/playlist per day (with several videos in there). Anything you do on Yt, especially in saturated verticals, you need to take a long term view and strategize accordingly. With respect to "in-stream" or "video discover ad", it depends on your purpose:
In-steam is used when you want to build brand awareness or spread a message across. It's usually used by known brands. Think of it this way, someone has clicked on a video to watch it, then here's one of your ads, that will take them away from the video they want to watch to your trailer. It better be a good trailer or video, otherwise they will be p****d that the ad took them to somewhere that didn't fulfil their expectations. You don't want your ad to kill their session time. If they click back to the previous video, you'll just get a low retention. If they close the browser tab, that's the death nail for your video and potentially channel. Avoid killing session times.
Video discovery is right sidebar and other placements that are less intrusive. If they like the thumbnail, they click it. It's generally in the viewing stream, and you'll be part of the session as they go to another video after yours.
3 months is nothing. For our channel, nothing happened for a good 6 months. Then there was a small blip. Then it took another few months to catch on. Some channels do it quicker, but you'll find the creators already have experience (parents have either their own successful vlog or other channels like Mom has a beauty/makeup channel) and they get those viewers over via verbals and in video links. Other ways channels grow quickly is they get their videos perfectly matched and timed to the crest of a super popular trend, get on suggested in progressively higher count channels, then execute flawlessly and professionally daily. 2 examples in the last 2 years: giant surprise eggs and bad babies have build a number of channels really fast and hard.
