Miss Cherry - the age requirement is 25, or 21 if your partner is 25 or over. Also, not to be rude, but you can't pick and choose the age of the child. When you become a foster carer you have to be willing to take any child that comes - and often there are sibling groups. Now, usually, you're not allowed to foster a child that is a similar age to your own. They often say there should be at least a 2 year age gap (if possible) either side of your child's age. Obviously that's not always possible, especially if you get an emergency case.
Soph - Emergency Fostering is just that - emergency. The child(ren) or young person will often come at very short notice, and usually will stay a day or 2 until a placement can be found (they like to make it as quick as possible so they child will setlle with their carer and not be too disrupted). Occasionally (and very rarely) that child will stay as long as a week. Usually in the case of an emergency social services will go to court the day after the child is placed as an emergency and get an emergency Care Order which lasts 48-36hours before they get an Interim Care Order. Then the child will either be moved, or if the foster carer they're placed with as an emergency has room for them, and are registered as short-term or long-term Fosterers then sometimes the child will stay with them. Often a lot of children go into Care as an emergency but an emergency order only lasts a few days until they can get an Interim Care Order
Colleen - In short, no you can't choose an age range. Because you're children are so young it's more likely you'd have older children, or sometimes Teenagers placed with you. This is because it can be very difficult for a child in Foster Care, and if they're placed around other children their age, they all start fighting for who deserves attention etc. As for whether they're completley "stable" or not ... Every child, and every case, is different. Children who have been badly abused can be completely withdrawn or sometimes extra hyper (to get attention). A lot of it depends on where they've come from and what's happened. Sadly most children in Care are damaged in one way or another. A Foster Carer's job is to do more than just provide them with a safe, stable home. They have to show that child what it's really like to be part of a family. They have to help the child make sense of why they've come into Care without bringing up too many distressing feelings. This takes time and trust.
What I would advise you though, mainly because your children are so young, would be to wait a few years. Young children find it difficult to understand the concept of fostering - especially as usually there will be lots of children in and out your house. Also, your children would have to share you with other children. These are children who potentially may need a little extra 1-2-1 time and will need plenty of time and space to understand things. Also, there's a lot of transporting Foster Children to contacts with their family, which may make your children upset or jealous that you spend so much time with them