Congratulations! I know adoption can often be a tough journey so great you managed to do it.
Some great tips in the thread already. When ours were nearly two we generally either went in Club or paid for a seat, but if you can’t afford it don’t worry.
Two things I would add. Firstly leave a lot more time/contingency time than you would without children. Kids have a habit of using it all then you are suddenly up against when you don’t want to be, plus every step of the airport process tends to take a bit longer.
Secondly, do plan but remember there is a randomness factor. We’ve had kids be as good as gold and/or sleep through late/long/delayed flights. And we’ve had them be grumpy/cry on short flights perfectly timed for them. Sometimes it is what it is. Most other passengers, especially parents, will appreciate you are doing your best and sometimes it just isn’t a kid’s day.
For what it’s worth we all board together at the start of boarding. I think our kids like the security of having everyone there and us doing things together.