Engaging autistic children in play can be a lot more challenging than with non-autistic children. In addition, play needs to reflect both enjoyment for the child, and assist development of specific personality traits and coping mechanisms.
Look for toys that stimulate their senses. Many children with autism have sensory challenges, particularly tactile defensiveness. Toys can be an excellent way to introduce tactile sensations in a low-key, non-threatening way. They don't have to wear, carry, eat (with the exception of children prone to pica), or listen to toys and that can be a very big bonus as they explore the items in their own way, and own time. Suitable toys might include:
Books with cloth, foil, yarn, etc. attached to them - you can even make your own
Blocks with raised lettering or numbers (this appeals to the ordering need as well)
Toys with bumps, fur, raised elements, ridges, etc.
Musical toys and toys that make sounds
Hard board books for children prone to tearing - allow them to tear the wrapping paper as much as they wish!
Choose toys that help social interaction development. Teaching all children cooperation through toys is an important rite of growing up. For autistic children, socially interactive toys are even more important for helping them to develop coping mechanisms when interacting with the wider world. Board games are excellent for this, especially when the whole family pitches in to play together. Focus especially on the issue of taking turns and not getting uptight about losing. All children need to learn these skills but the frustration element can be very intense for autistic children.
Find toys that help to develop motor skills. It's really no different from what all children need but you will probably have to face tactile defensiveness, inability to balance, fears, etc. Painting and drawing are good choices, although the paint might upset some autistic children if it gets on their body, so it might be best to use brushes and avoid fingerpainting for such children. Developing balance might be tricky if your child refuses to ride a tricycle or bicycle. A lot of encouragement and patience will be required, as well as understanding that it might never happen. Trampolines are excellent but make sure it is safe and always be present.
Always be considerate of the level of autism. Less complicated toys are better for children who are low-functioning autistic; simple push-button, open and use toys are best. For higher functioning autistic children, building, creating, discovering, connecting, etc. toys are generally fine. For some autistic children who demonstrate a clear preference for a single interest, you can give toys that reflect this interest. This will definitely engage them. The only risk here is that they can rely too much on their single interest and not be challenged to try and engage in other areas where their interest lacks.
Don't overdo the functional play. There are times during which it is fine to let your child simply enjoy a line of toys that is pure fun. The difficulty arises when the child prefers this line to all else, so monitor any addictive preferences carefully.
Select quality over quantity. Too many toys is always too many toys. For autistic children, it can feel overwhelming and crowding. It is better to choose one good quality toy over many cheaper toys that will create great clutter. If you hit the right choice, that one toy will provide many hours of enjoyment.
Search online. There are numerous stores catering to toys for autistic children, offering advice and good ideas. There are also many, many guides on what toys to get for autistic children. Have a good read to inform yourself and apply the most appropriate ideas to suit your child – every child is different, and every form of autism is different, and you know your own child's needs and interests better than anyone else.
Let the child go with you. My brother is autistic, and when Christmas shopping, we let him go with them- he will pick a toy he likes, and even use his words sometimes- "I want fire truck."
People who don't understand autism will tend to give "age-appropriate" gifts. Autistic children develop at different rates and may not be ready for the gifts. Check your irritation; people mean their best and only family and best friends should be informed about the need to be conscious of developmental stages. Everyone else - just put their gifts in storage until your child is ready. If the the toy is so unsuitable as to never be of any use, re-gift it quietly.
As with all children, avoid using the TV as a play device. Moderation is key for all children.
Note that while some autistic kids are oversensitive to stimulation, others are under-sensitive, and would love finger paints and other sensory stimulation such as bouncing or swinging.
Don't be afraid to ask the parents of an autistic child what an appropriate gift might be. Oftentimes they may be able to tell you an age range of toys that might be more suitable than their actual age.
Spinning toys can be very attractive to autistic children but can also be addictive and difficult to remove from the child; this means that other toys are not played with in preference for the spinning toy.
Never get objects that shatter when dropped. Not only is this dangerous but the resulting hullabaloo from a very upset child is never worth it.
If you're giving a gift, don't be offended when it goes unused. The child's experiences of the world differ from yours and what might seem fantastic to you might be scratchy, noisy, overly bright, or uncomfortable for the child. This is something to remember for all gifts to children; their personality isn't yours!