You do not have to have twins to buy a twin pushchair, twin pushchairs are designed specifically to accommodate two toddlers, babies or young children. Not many people have twins in the UK but there are lots of similar aged siblings.
Many parents choose to have their children close together, it is much easier young ones of a similar age as they tend to play together more if there is less of an age gap. With very young children they go through stages and tend to want to walk a little distance and then get tired and want to be pushed in the pushchair again. If you already have a baby in the pushchair then you will need a twin pushchair for both of them.
There are two different types of twin pushchair, the first is the traditional pushchair which looks like two single pushchairs joined together. This has the advantage of allowing both the siblings to be next to each other so they can play and interact with each other. As they get a little older it also reduces the amount of squabbling as both sears are exactly the same.
The down side to twin pushchairs is that they are twice as wide as a standard model. This of course means that it is more difficult to get through many doorways. Access can be a problem if you need to get in and out of shops or indeed other peoples homes without having to take the children out of the chairs.
The other option is to choose a tandem pushchair, this again has two seats but rather than being side by side one seat is in front of the other. The obvious benefit of this is that it is the same width as a single pushchair and so allows you easy access through doorways.
Whilst it may be more convenient for the parents it can cause tantrums with the young children as they argue over who goes in the front or back. The seating is set up so the rear seat is slightly raised above the front seat. This is to allow the child sitting in the rear to have a view ahead and so that the pushchair does not have to be as long.