The children were happily smooshing the playdough together.

smooshing 是动词 smoosh 的现在分词形式。smoosh 是一个非正式用语，意思是"挤压、揉捏、把东西压扁或混合在一起"，通常用来描述用手把柔软的材料（如橡皮泥、面团等）揉捏或压扁的动作。