Could you spend a little one on one time with each of them? Have a box of "special" toys or a tv show for the one who isn't getting mama time at the moment. With your ds you could read, do worksheets together, a game or a craft. Something to give him more mental stimulation than what he's getting from your dd. Then spend some time with her doing things she enjoys.
You could also separate them for a small period of time during the day. My ds and dd are similar ages as yours and a little time away from each other really helps them.
You could also all do things together, like baking, simple science experiments, crafts or story time. My ds and dd are best friends but at the same time can be worst enemies. Breaking up their play time helps them to have more fun and stimulate their imaginations
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