The best thing I've found for my little one (1 year old) for solo play is to give her something that isn't designed to be a toy and also that she hasn't seen before. Things like kitchen utensils and mixing bowls, big cardboard boxes she can climb in, random objects that seem safe... all those things she loves to play with. If it is designed to be an actual toy she gets bored more easily! My 4 year old will play by herself really well for a LONG time with arts and crafts and legos and that sort of thing and has been doing that for awhile.
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