Do NOT install yer child seat sideways. Their body will not be able to use the seat to distribute the force to the seat and you could possibly injure them severely if not kill them.
Make sure the child seat is rear facing as long as possible. Some people go by weight to forward face their child...studies show that the child is safer facing rearwards in their child seat in frontal impacts as there is more material to distribute their weight and cradle their head/neck from being strained.
The jump seats should be fine. Just make sure you git the best seat you can afford fer yer child. Congrats on yer upcoming joy (child...that is!)
