Is it large enough for a small 5 year old?
Yes, it is. We have a 8 years old that loves it.
Is this tray solid enough for my child to draw on with pen and paper?
Yes, there is a solid plastic inside the zipper that make the surface sturdy and flat.
Will this work for rear-facing carseats?
Yes, it will work. This travel lap tray is free standing and is compatible with most commercial car seats: (rear facing) car seat, booster, stroller and push chair.