Your infant has a lot of work to do in his first year, building strength and control in his body and limbs for the day he learns to sit up, then crawl and eventually walk. He doesn't realize it, but he's been preparing these muscles since the day he was born. You can help him along the way with some games and exercises that stimulate his gross motor skills while giving the two of you some quality time together.
Give your infant lots of opportunities to lie on lie on his tummy, as this helps strengthen the muscles in his neck, back and torso for sitting, crawling and walking. Encourage him to lift his head by waving a toy or calling to him; he'll eventually push up onto his arms. Do not leave your infant unattended on his tummy, though, as there is a danger of suffocation.
Place or wave toys just out of your infant's reach, while he's lying on his back or tummy, to help him learn to roll over. Rock him from side to side to help him experience the sensation of rolling. Babies can learn to roll over starting at about 3 months. Once your baby is able to balance on his hands and knees, you can use this same technique to encourage him to crawl forward.
Place your infant in a jumper or exersaucer and watch his delight as he manages to use his body to make it move; this teaches him how control his own body movements for a purpose. Do not leave your baby unattended in one of these devices.
Encourage lots of leg kicking to help your infant build up her leg muscles for the future. Do this exercise by lying her on her back and playing games such as tickling her toes or moving her legs back and forth with your hands.
Show your infant how to use her legs to pivot herself around on her back or tummy by moving them in a scissor-like movement. Remember, your baby should never be left alone on a high surface.
Hold your baby in an upright position under her arms and allow her to experiment with carrying her own weight on her legs. Don't force her to do this, but you can see if she is ready at about 6 or 7 months. This position is also good for a little bouncing. When she is able to hold her own weight, you can help her walk along holding her under her arms or by the hands.
Wave toys above your baby as he lies on his back, to help him take control of his arm movements. This game encourages him to grab at the toys and figure out how to make his arms go where he wants them to.
Teach your baby how to use his arms to clap, wave and shake toys by repeating these movements for him to imitate; babies love copying! Your infant will enjoy watching these actions from birth, and it may only be 3 months by the time he has started to master them himself.
Pull your baby up slowly by his arms into a sitting position from lying on his back to strengthen his arms. Wait until he can support his own head, after about 3 months, before you attempt this exercise. As his arms become stronger, show him how to balance on his hands and knees ready to crawl. When he starts to move -- whether it is crawling or bottom shuffling -- you can hide toys around the room and challenge him to find them to encourage him to keep working on these skills.