As a mom of many, I can say that young children learn their faith by watching you live yours.
Activities are great reinforcement, but it's the daily life of a faithful father that will transmit the reverence, awe of God and love of God to his children.
Other posters have given you wonderful suggestions.
I'd recommend letting them see you pray the rosary and general prayers, read your Bible or missal, attend Mass, use sacramentals and provide the children with age appropriate religious literature.
Put a Holy water font or several in your home so the children get in the habit of blessing themselves. Let the older ones take turns leading a decade of the rosary. Make a celebration of Name days and anniversaries of their baptisms. Teach them about their patron saints and the other saints. Keep it short, sweet and simple because they are young. Take them to a perpetual adoration chapel to say hi to Jesus. Again, it will be a short visit, maybe a wee bit noisy one, too, in the moment, but it will teach them to appreciate and value their Faith. Oh, what about a home enthronement to the Sacred Heart? Have a special area in your home for a home altar. A little statue of the Holy family always appeals to little ones.
There are so many little things you can do right now. Once the kids are older, they can get more involved. (Like altar serving once your 7 year old receives 1st Communion.) take your time. The little actions will build a strong foundation for the future.