Unanticipated Exercise.

So my 4 year old son has a play date over for the day while her mums in work. They are having great fun putting things together all over his bedroom floor to make pictures of different things. It's really very cute & I am thrilled with their creativity, but, they keep calling me upstairs to look, it's only 9.05 & I am already worn out! Heaven help me by 4.30 when her mum is picking her up!