Elliott loved the baby gym too- we had one which you could hang different things on so I kept moving things around and putting new toys on. I also tied things like balloons, silk scarves and streamers, chiming bells etc out of his reach but over his head and then lay next to him and biffed and blew them. He still loves mobiles and always blows at light fittings or anything hanging from the ceiling in case they move! I also read to him a lot as I didn't know what else to do with him and of course he didn't wriggle away at that age! He particularly loved Dr Seuss at that age because the pictures are quite bold and often 2 colours only, he also liked the sound of things like "Green Eggs and Ham" because of the pace and patterns of language I think. He's off those at the moment and more into books with things to feel and things I can act out like tickles and yawns etc.
We also used to lie him on the bed and move his arms and legs to music- he loved that! Mostly it was "Hands up baby hands up!" (showing my age!) or Yellow Submarine! We also did this thing where we pushed down on the mattress under him so that he bounced up within our arms if you see what I mean- he really loved this but it tired me out!
Hope that helps!
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