Playing in the paddling pool? Grab some cups, bowls and jugs and let the children explore which containers hold the most/least water. They don't need to be able to read scales, they may choose to measure based on how many cups or jugs something can hold. In my experience, one of the things children find most baffling about capacity is that containers of different shapes and sizes can hold the same amount of liquid. You could challenge them to find the pots which both hold 6 cups of water (for example).
Last but not least, go outside and be active, family bike rides, scoot/skate/jog round the park. Go for a walk. Go camping, it's a cheap (if you already have all the kit) but fun way to get away together. Whatever you choose, try to take time to look at the world through the eyes of your child, ask questions, answer questions, but most of all, have fun!