Second the package deal, so much easier having everything sorted for you.
I tend to book packages online but the high street travel agents where you can go in and chat will probably be more helpful because you can ask as many questions as you want and they’ll walk you through everything. Hays Travel have a lot of branches and good reputation.
Personally I would look at family friendly resorts in Spain, not too long a flight, most people speak English, easy enough to pick up food/drinks/supplies in the local shops if you forget anything, resort pools tend to be decent and other kids around for yours to play with if they wish to! Then branch out further once you feel more confident!
And well done for being brave!