Is the child mobile at all? If so balloon move slowly and are directable, so you can hit it close to where the child is. This will improve strength and motability.
Suitable toys and free play are good, but you will want to schedule some organised play if you are to be together for more than half an hour.
Making noise is good, with instruments or pots and spoons. Nursery rhymes, peek-a-boo and waving your hands about (if you can do these together, all the better) are good for kids. Don't underestimate the entertainment value of slapstick, put on a show, mess about and fall over, dance. Or maybe it's just my dancing that has kids in stitches
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Handling keys, spoons, gloves and anything else that they can't swallow and isn't deadly allows them to explore objects they see everyday, yet do not know what they do.
Mum2bless let your imagination run wild and then narrow the options down by assessing their safety.
An important thing that is rarely mentioned is this: Enjoy whatever it is you do. Teaching children how to have fun is just as important (if not more so) as developmental tasks.