Of these two entry level plastic canoes, the Pelican in this case is the better paddling canoe. the Old Town Rockport is the lowest priced Old Town at $539 list and is the fattest tandem in their line at 42". At 14' length, the 42" width makes it one stumpy little tandem. Yes it has 3 seats, but that does not make it the choice for paddling with youngsters. In fact its width is what makes it less desirable. A narrow shouldered youngster with a short paddle seated in the middle of the bow seat in such a fat little canoe has a long reach to the water on either side and will tire quickly. The paddle stroke will be more of a sweep stroke than a forward stroke and not do much for propelling the boat forward, but do a lot to turn the short little canoe sideways.
The 15'6" Pelican is slimmer and longer, and will paddle better than the Rockport. The seat will still be a reach to the water for the bow paddler, but much easier to achieve a vertical stroke than in the Rockport. Hang a sling seat or drop-in seat for the second youngster behind the bow seat for best trim and let both paddle.
Both these canoes are best suited to short trips with short carries to the water. Both are heavy canoes in the 80# range, but that is the price paid for the low purchase price. Spend some of the money saved on good light paddles with grips to fit the small hands of the youngsters. Look at Foxx and Sawyer for quality light paddles that fit youngsters hands. A cheap paddle only tires them out, a poor fit rubs their hands, and a heavy paddle is too tiring for the lifting on the recovery phase of the paddle stroke.