Physical activity classes - usually run as a course of one session a week in 10 or 12 week blocks - are for babies as soon as they have started crawling, right up to children in the early years of school. They generally take place in church halls, gyms or any other large room, and last about 40 minutes.

Activities for the youngest age group are very low-key, with an emphasis on showing you different ways you can physically play with your baby.

As babies move on to the toddler stage and beyond, classes should become more physically challenging. Ideally the activities will incorporate a mixture of familiar equipment (perhaps a ladder and slide) with added dimensions, such as a trampoline or stepping stones, a tunnel to crawl through or a beam (even if it is lying on the floor) to balance on. There may also be games which include catching and throwing, usually with slow-moving objects like balloons to make it manageable for young children, and there will also be early gymnastic movements such as forward rolls (going head over heels), swinging along under ladders, skipping and jumping.

Sessions often begin and/or end with a 'music and movement' time. During this segment children are encouraged to listen to music and move appropriately to the rhythm, speeding up for fast music, slowing down for more sombre tunes. There may also be singing, which could include action songs where the children act out the words, like 'Jack jump over the candlestick', and counting songs, like 'Five fat sausages frying in the pan'.

At first, you will be expected to take an active, participating role, helping your child to negotiate the equipment and sing along. Once your child reaches pre-school age (about three or four), most classes will be run more formally, with a number of staff to a small group of children, with parents or carers simply as bystanders.

Early on, introducing your baby to new physical experiences is all about learning and letting her explore the world around her and discover how to use her body. Your interaction with her is the crucial element - as in all things, she looks to you to help her.

As time goes on, you will notice that children who are given lots of opportunities to practise different physical skills in an encouraging environment will have had the chance to hone their agility, balance and co-ordination and this can have a number of positive knock-on effects. One is that they are safer when they're let loose in a playground. They will have been taught how to go up and down ladders properly, they will know how to right themselves if they start to lose their balance on a piece of equipment (say, a climbing frame), they may even have been taught how to fall safely. Their general level of co-ordination will mean they are better able to use the equipment and so get more out of the experience.

Another effect is your child's heightened physical ability and awareness and this, in turn, gives her independence. The child who can feed and dress herself feels a boost to her self-esteem and, when she reaches school-age and finds she is one of the children who can kick a ball into goal, catch well, or is one of the first to ride a bicycle, her confidence will notch up another level.

Finally, physical play classes can teach young children the meaning of many positional words such as left, right, in front of, behind, forwards and backwards.

You ought to be able to try a class before having to sign up for a whole course, but if not, ask if you can watch a session.

•   Look for a high ratio of staff to children and certainly not more than eight children per adult
•   Staff should be specifically trained and should offer a well-thought out programme - ideally, they will receive regular top-up training sessions to keep them abreast of new ideas and developments
•   You and your child should be made to feel welcome and, as the session gets going, look for signs that there is lots of support, encouragement and praise given to the participants - not just for achieving but simply for having a go
•   The room needs to be large enough that children don't run the risk of bumping into each other for lack of space, and it should be light and well ventilated (and adequately heated for winter)
•   Satisfy yourself that the equipment is in good condition and that the safety of the children is always paramount. For instance, are there cushioned mats under climbing equipment? Do staff make sure children have taken their socks off before they start running around?
•   Finally, does it look like fun and does your child want to have a go? A good class will have lots of child appeal and that, after all, is what you're there for